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Larval nematode parasites (Spiruroidea: Cystidicolidae) are recorded for the first time in Octopus vulgaris Cuvier, 1797 in the northeastern Atlantic Ocean. Prevalence was 16% and mean intensity was 1.46 worms/host. Body length of larval nematodes ranges from 8.3 to 9.3 mm, with a distance from the anterior end to nerve ring from 187.5 to 200 microm, and to excretory pore 194.6-350 microm. Anatomical characteristics, such as deirid, nerve ring, cephalic alae, excretory pore, pseudolabia amphids, sclerotized protuberance, and anus, examined using light microscopy (LM) or scanning electron microscopy (SEM), are illustrated. The nematode was designed as a cystidicolid "Type A" larva. The hemocytic infiltration present in the host tissue around the nematode capsule and the mechanical compression in the infected organs denote the pathogenicity of this nematode. In the study area, O. vulgaris may play the role of an intermediate or paratenic host in the nematode life cycle.

The temporal and spatial dynamics of the recruitment of Halipegus occidualis by the green frog, Rana clamitans, suggest that infections are acquired through predation on odonates, which become infected by feeding on ostracods. Discrepancies in the literature regarding the life cycle of H. occidualis prompted the investigation of the status of the odonate naiad as an obligate third intermediate host. Infected ostracods were examined at weekly intervals to follow the postcercarial development of the parasite. Four-week-old "mesocercariae" were morphologically similar to metacercariae recovered from natural odonate infections and were infective to green frogs. Passage of the parasite directly from the ostracod to the frog host did not affect the infectivity of the worms or the period of development required to reach the adult stage. Thus, development into the metacercaria takes place within the ostracod, with the odonate acting as a paratenic host. The paratenic transfer of metacercaria is a common phenomenon among hemiurid trematodes, indicating a primitive 3-host cycle for the group, with opportunities for host capture being facilitated by a generalist strategy for the metacercariae.

This paper represents the first documentation and description of Pachysentis canicola cystacanths and the first report of a Pachysentis sp. in a paratenic reptile from the Americas. The western diamondback rattlesnake (Crotalus atrox) is also listed as a new host for tetrathyridia of the cyclophyllidean cestode (Mesocestoides sp.) and for the cystacanths of the oligacanthoryhynchid acanthocephalan (P. canicola). Six rattlesnake specimens were examined from Nolan County (32.30 degrees N, 100.39 degrees W), Texas. Four snakes (67%) were found parasitized with between 3 and 16 (mean 7) encapsulated tetrathyridia and 1 host additionally was infected with 6 P. canicola cystacanths within its mesentery.

Two types of third-stage nematode larvae (most of which were encapsulated) were collected from the abdominal cavity and liver of the freshwater fishes Etheostoma fonticola, Etheostoma lepidotum, Cichlasoma cyanoguttatum, Lepomis auritus, Lepomis sp., and Gambusia affinis in Texas and are referred to the genus Falcaustra. This is the first record of Falcaustra larvae from fishes, and their presence may reflect the importance of fishes as paratenic hosts of turtle parasites in this genus.

The possibility exists that paratenic hosts play a role in the life cycle of various Dracunculus species. In the present study, we established that tadpoles of 2 genera of frogs (Xenopus and Rana) were capable of ingesting copepods infected with third-stage larvae (L3) of Dracunculus insignis. Once ingested, the L3s migrated from the gut to the somatic tissues of the tadpoles. In Xenopus, the dracunculid larvae persisted through the metamorphosis of the tadpoles into adult frogs. These observations confirm the concept that paratenic hosts, such as tadpoles or frogs, may be important means of transporting infective larvae of Dracunculus species up the food chain and facilitate transmission to the definitive hosts.

1. This paper examines the population biology of two related species of bothriocephalid cestodes, parasites of teleostean fish, which live in sympatry. One species, Bothriocephalus barbatus, needs in its life cycle only one obligatory intermediate host, a copepod. The second species, B. gregarius, needs the same intermediate host first, but also utilizes a non-obligatory paratenic host, which is a gobiid fish. In the case of B. gregaring, definitive hosts can be infested via the intermediate host or the paratenic host. A simple mathematical model was built to investigate the effect of the addition of a paratenic host into the life cycle of a parasite. 2. Results of the simulation clearly demonstrated that the maintenance or absence of infectivity of cestode larvae in the paratenic host could explain the observed levels of infection in both definitive hosts. 3. Acquisition of paratenic hosts has two advantages: the recovery of lost infective stages in a previously non-suitable intermediate host, and an increase in the time of infection during which the definitive host could be infected as the result of eating copepods in its planctonophagous juvenile existence and by eating gobies in its predaceous older stages. 4. Using the basic transmission rate as a measure of fitness, we also investigated the possibility of maturation of B. gregarius in the paratenic host, e.g. the acquisition of a new definitive host by the parasite. Basic transmission rates and numerical simulations suggest that there is no benefit for the parasite in evolving towards this strategy

The original description of Polyacanthorhynchus kenyensis Schmidt and Canaris, 1967 from 2 species of fish in Lake Naivasha, Kenya was primarily based on measurements of 2 male cystacanths. That description is herein emended based on the availability of a larger number of immature worms of both sexes obtained from the freshwater teleosts Orechromis leucostictus, Tilapia zillii (new paratenic host records), and Micropterus salmoides. A secretory function for the apical organ is suggested.

Encysted acanthocephalans belonging to the genus Centrorhynchus were found in the body cavities of Sorex araneus (common shrew) and Sorex minutus (pygmy shrew) from Boxworth, Cambridgeshire, U.K. Fifty percent of the male S. araneus and 67% of the male S. minutus examined were found to be infected, with the mean intensity (+/-SD) being 54.3 +/- 91.3 and 14.7 +/- 18.4, respectively. The species of Centrorhynchus in the shrews may be Centrorhynchus aluconis, which is distributed widely in tawny owls, Strix aluco, in the United Kingdom. Shrews appear to serve as paratenic hosts for C. aluconis.

The histopathologic alterations occurring in mice, hamsters, turtles, and a frog were described following experimental infection with nymphs of Sebekia mississippiensis. Initially, nymphal migration caused traumatic tissue damage and hemorrhage characteristic of larva migrans. Subsequent inflammatory responses included cellular infiltration with eosinophils, macrophages, and lymphocytes, and fibrotic encapsulation of the nymphs. Dead nymphs were surrounded by a necrotic granulomatous response similar to that reported previously in humans and other animals. Differences were not seen in animals given single or multiple infections, but mice and hamsters exhibited a more marked inflammatory response than turtles. Overall, the histopathologic response to nymphal infections resembled those seen in infections resulting from ingestion of eggs, and both sources of infection should be considered in epidemiologic investigations of naturally occurring pentastomiasis.

10 coyotes suggests that this coyote was infected at an early age, probably by exposure to larvae passed by its dam. A related metastrongyloid, Filaroides martis (=F. bronchialis), in mink (Mustela vison) uses gastropod intermediate hosts, and mice can serve as paratenic hosts for the final infection (Dubnitski, 1955, Karakulevod. Zerovod. 8: 51; Anderson, 1962, Can. J. Zool. 40: 893-920). Further investigations of the possible role of prey species in the life cycle of 0. osleri in coyotes are warranted.

Oslerus (Oslerus) osleri (=Filaroides osleri) is a widely occurring, tracheal parasite of wild canines (Holmes and Podesta, 1968, Can. J. Zool. 46: 1193-1204; Thornton et al., 1974, J. Wildl. Dis. 10: 232-236; Morrison and Gier, 1978, Ibid. 14: 314-316; Samuel et al., 1978, Can. J. Zool. 56: 2614-2617; Pence and Meinzer, 1979, Int. J. Parasitol. 9: 339-344). In domestic dogs, 0. osleri has been reported from several continents, but is uncommon (Mills, 1967, J. Sm. Anim. Pract. 8: 37-43). Little is known of the natural life cycle of 0. osleri (Mills, loc. cit.), but 0. osleri has been experimentally transmitted directly from dog to dog using first stage larvae (Dorrington, 1968, Onderstepoort J. Vet. Res. 35: 225-285; Polley and Creighton, 1977, Vet. Rec. 100: 136-137). Price (1928, J. Parasitol. 14: 197) suggested that dogs were accidental hosts for 0. osleri, the normal hosts being wild canines; however, attempted transmission of 0. osleri from coyotes (Canis latrans) to domestic dogs has not been reported. The purpose of this study was to compare the success of direct transmission of 0. osleri (coyote origin) in coyotes and domestic dogs. Rats also were inoculated with larvae (coyote origin) to determine a possible role of rodents as transport or paratenic hosts. Large nodules containing live adult 0. osleri were separated from the tracheal mucosa of a wild-caught, adult coyote from Whitman Co., Washington. Adult female worms were teased apart and macerated in a small quantity of 0.95% phosphate-buffered saline (PBS). Embryonated eggs were washed through a 100-mesh sieve into a 250-ml beaker with 150 ml PBS. Eggs were stored at room temperature (25 ? 2 C) in a covered beaker and were examined on days 6, 7, and 8, by which time many eggs had hatched to motile 1st stage lar

Paratenuisentis ambiguus is described from natural infections in adult eels and from laboratory infections in sticklebacks and juvenile carp and rainbow trout. In captured eels, female worms kept reproducing in the laboratory for at least 1 mo. In the 3 small laboratory hosts female worms did not release eggs and longevity did not exceed 3-30 days. It is concluded that the small fishes were unsuitable final hosts. Worm penetration into the intestinal wall of all hosts was shallow. Thus, the small fishes also proved to be unsuitable paratenic hosts. The worms ruptured the intestinal mucosa and the underlying tunica propria and they often seemed to change their sites of attachment. The proboscides carried an osmiophilic surface coat that seemed to be supported by liquid drops from necrotic host tissue and by osmiophilic material apparently discharged from pores in the worm's proboscis hooks. The coat contained lipids, polysaccharides, and/or proteoglycans and likely other substances. Around the hooks the proboscis tegument harbored conspicuous cisternae of rough endoplasmic reticulum as is typical for cells with secretory function. Mostly, the worms were found with semi-invaginated proboscides. The resulting cavity inside the proboscis seemed to collect lipids and other remnants of host cells from the lesions caused by the worms. Whether the apical hollow might function as a gastric cavity is discussed.

Cestodes of 4 species and nematodes of 9 species were collected from 75 bobcats, Lynx rufus (Schreber), in Nebraska from 1977 to 1979. Of these 75, 11 were trapped from 6 border counties in 3 border states: South Dakota, 7 carcasses/3 counties; Kansas, 3/2; and Wyoming, 1/1. Helminths recovered included: Mesocestoidescorti Hoeppli, 1925 (15% prevalence), Taenia rileyi Loewen, 1929 (67%), Taenia pisiformis (Bloch, 1780) Gmelin, 1790 (27%), Taenia macrocystis (Diesing, 1850) Luihe, 1910 (19%), Physaloptera praeputialis von Linstow, 1889 (55%), Physaloptera rara Hall and Wigdor, 1918 (32%), Toxascaris leonina (von Linstow, 1902) Leiper, 1907 (31%), Toxocara cati (Schrank, 1780) (39%), Ancylostoma tubaeforme (Zeder, 1800) von Linstow, 1885 (5%), Pterygodermatites (Multipectines) cahirensis (Jagerski6old, 1909) Quentin, 1969 (1%), Vo- geloidesfelis (Vogel, 1928) Davtian, 1933 (7%), Cylicospirurafelineus (Chandler, 1925) Sandground, 1932(12%), and Capillaria aerophila (Creplin, 1839) (4%). One bobcat was not infected; 74 had 1 to 7 species (xc= 3). Simpson's index for helminth species was moderately low (0.12), indicating a relatively diverse helminth fauna. Mean levels of infection between prominent species pairs and within each species were compared with bobcat sex and age differences using Student's t-test. Mean intensity of Physaloptera praeputialis was significantly (P < 0.01) greater than that of Toxocara cati; mean intensity of Mesocestoides corti was significantly (P < 0.01) greater than that of all other prominent species. No significant intensity differences were indicated among bobcat sex and age categories. G-tests computed for prevalence of prominent species with bobcat age indicated no signif- icance. Prevalence of prominent species and bobcat sex indicated Physaloptera rara was significantly (P < 0.05, 1 df) more common in females than in males; all other prevalence distributions for sex were not significant. Prevalence between species pairs was analyzed among 8 helminth species; highly significant associations (P < 0.005, 1 df) were found among 5 pairs. Dependent positive relationships between spirurid nematodes and taenioid cestodes did not occur. No relationships were ascertained between helminth infection and bobcat diet. Comparison of helminth fauna in bobcats from Nebraska and 7 geographic areas in North America indicated a high prevalence of Taenia, Physaloptera, Toxascaris, and Toxocara. This indicates the primary use of rodents and lagomorphs as paratenic or intermediate hosts as well as common food sources for the bobcat.

The term amphiparatenic host was coined originally for hosts of Alaria marcianae that as adults are paratenic hosts, but as juveniles serve as definitive hosts. In this study the concept of amphiparatenesis is placed in a theoretical context, maternal transmission shown to be the basic mechanism, and the concept extended to include Toxocara canis, T. cati, T. pteropodis, Neoascaris vitulorum, Ancylostoma caninum, Uncinaria lucasi, various species of Strongyloides, Pharyngostomoides procyonis, and P. adenocephala. Alaria marcianae mesocercariae were used in a feline model to show that male and nonlactating female cats are definitive hosts, but lactating cats are primarily paratenic hosts. Inoculation of 1 female cat resulted in the infection of 21 of her offspring via the milk over the course of 5 litters and after a 3-yr period she still had viable larvae in her tissues. The ability of parasites to remain immature in amphiparatenic hosts is believed to be an adaptation on the part of the parasite to promote dissemination through maternal transmission and not the result of resistance, immunological or otherwise, on the part of the host. The amphiparatenic concept has important implications that include: the use of pregnant and lactating females as reservoirs of infection for the offspring; infection transmitted through a contagious transplacental or transmammary pathway; a parasite population structure in which adult worms are in greater abundance in neonate than adult hosts; and the effective control of parasites utilizing this strategy proving to be very difficult.

The transmission of nematode parasites of vertebrates is reviewed with special reference to the phenomena of monoxeny, heteroxeny, paratenesis, and precocity. Monoxeny is divided into 2 types. Primary monoxeny assumes that there was never an intermediate host in the transmission. Secondary monoxeny assumes the loss of an intermediate host during the course of evolution and its replacement by a tissue phase in the final host. Heteroxeny, or the use of intermediate hosts, is a common feature of many nematode groups. The Spirurida utilize arthropods, the Metastrongyloidea molluscs, and Ascaridida arthropods and vertebrates. Paratenesis, or the use of transport hosts, is a common feature of the transmission of nematode parasites of carnivores. It is postulated that in some instances paratenic hosts have become intermediate hosts and replaced the original intermediate host. Precocity in the development of nematodes in intermediate hosts (including what may have been paratenic hosts) is defined as growth and/or development beyond the expected. Its occurrence among the nematode parasites of vertebrates is reviewed. It is regarded as a transmission strategy which accelerates gamete production in the final host. Precocity could also provide the mechanism for the transfer of a parasite from a predator final host to a prey final host.

Echinorhynchus pomatostomi Johnston and Cleland, 1912 is redescribed from the holotype, ju- veniles obtained from bird paratenic hosts, adults from feral cats in Australia, and Felis bengalensis in Borneo i is the first report of the adult and definitive host. The species is placed in the genus Oncicola, thereby becoming Oncicola pomatostomi (Johnston and Cleland, 1912) comb. n. The zoogeography of the species is expanded to both coasts of Australia, Luzon, Sabah, and Malaysia.

Transmammary infection with Alaria marcianae mesocercariae was demonstrated using mice as model, paratenic hosts. Prenatal transmission was ruled out because neonates removed immediately postpartum from infected dams were never infected. Mesocercarial distribution in virgin females and in females examined immediately postpartum showed no marked preference for the mammary glands. In contrast, infection of neonates that were allowed to suckle on infected dams was absolute, and the number of mesocercariae in the mammary glands of postparturient dams that suckled their young was increased significantly. These experimental observations were coupled with other observations on paratenic hosts to outline the pathways open to mesocercariae in gravid hosts. The term amphiparatenic host is coined for those host species that are paratenic hosts as adults, but as juveniles can serve as definitive hosts.

In the laboratory fingerlings of goldfish and carp as well as adult sticklebacks (Gasterosteus aculeatus) were infected with the palaeacanthocephalan Acanthocephalus anguillae. The fish were killed from 5 to 90 days later. In goldfish, worms began perforating the intestinal muscularis within the first 5 days postinfection (DPI). From about 50 days they were also found in toto inside the peritoneal cavity where they had become covered by a precipitin-like coat. Disintegrating dead worms always were enclosed by a granuloma consisting mainly of macrophages in different maturation stages. In carp intraperitoneal worms were recorded as early as 10 DPI. They provoked a heavy eosinophilic reaction and degenerated within a few days. In stickleback the recovery rates were very low; only 1 worm of 10 DPI was found just penetrating into the peritoneal cavity. The worms did not reproduce in any of the 3 hosts. However, female worms with copulatory caps were found, indicating that they had been inseminated. It is suggested from these results and from the literature that A. anguillae has a low ability to use paratenic hosts in its life cycle.

The persistence and precise location of Ancylostoma caninum larvae in tissues of vertebrate paratenic hosts and the nature of host responses were studied in mouse, cat, and monkey. Mice were infected percutaneously and examined at various intervals up to 260 days after exposure. Long-persisting larvae were found only in the muscles. Histologic sections revealed that within 4 hr after exposure some larvae had migrated through the skin and had entered individual fibers of the underlying muscles. After the 1st day nearly all larvae found in muscles were within fibers. Granuloma formation and encapsulation were not observed, suggesting that inside the fibers the larvae produced no direct inflammatory reaction. Only diffuse infiltration of inflammatory cells was observed in muscles and this appeared to be in response to destruction of muscle fibers. Larvae were similarly located in muscles of a cat and a rhesus monkey examined 16 and 17 days, respectively, after cutaneous exposure. The histologic changes observed in muscle fibers invaded by A. caninum larvae are similar to those observed in early Trichinella spiralis infections. The larvae of A. canninum lying coiled within the muscle fibers also bear superficial resemblance to the larvae of T. spiralis. A. caninum larvae were also recovered by tissue digestion from muscles of naturally infected dogs, which suggests that larvae reside in this location in the bitch prior to transfer to the neonate via the milk.

penetrated the liver showed no noteworthy changes except for GPT, which increased up to 170 Karmen Units at 3 and again at 10 wk after exposure. Although the significance of this change is not fully understood, liver damage may be involved. Several species of mammals as well as coldblooded vertebrates have been shown to act as the paratenic hosts, suggesting a broad paratenic host-range and suggesting that humans run the risk of exposure to this parasite. al species of mammals as well as cold

Pomphorhynchus bulbocolli Linkins in Van Cleave, 1919, was considerably more common in fishes of the river-connected Tichigan Lake than of the landlocked Silver Lake, southeastern Wisconsin. It is reported from 17 species of principal, accessory, and occasional definitive hosts (new record in Moxostoma carinatum) and from 13 species of paratenic hosts (new records in Amia calva, Ictalurus punctatus, Lepomis cyanellus, and Pomoxis nigromaculatus). Infection patterns were influenced by fish species, feeding behavior, temperature, availability of intermediate host, type of water body, fish movement, and changes in fish host community. Host roles are not fixed but are often interchangeable. A seasonal cycle in prevalence, intensity, and maturation was evident, with greatest abundance and maturation during summer and recruitment during summer and autumn. Recruitment of new infections, development, and release of eggs, however, occurred all year. Sex ratio changed from near equal in new infections to one more highly in favor of females in older adults. Female fish were considerably more frequently and heavily infected than males. No relationship with fish age (size) was evident. Worms were mostly attached in posterior intestinal locations but initial establishment sites correlated with temperature. Translocation of P. bulbocolli due to competitive exclusion in concurrent infections was not observed. The significance of extraintestinal larval forms in the cycle of transmission was noted.

Mesocercariae of Alaria marcianae were removed from snake paratenic hosts and fed to domestic cats. The cats were necropsied at specified intervals, the parasites recovered, and studied by SEM. During the prepulmonary phase of migration in cats, mesocercariae recovered from the stomach wall, abdominal cavity, diaphragm, liver, and heart underwent no tegumental modification compared to those fixed immediately after removal from the paratenic host. The mesocercaria resembled the body of an enlarged cercaria. The oral sucker was encircled by 14 or 15 rows of simple, posteriorly directed spines. Similar spines were also located along the margins of the venter and equatorially at the level of the acetabulum. This spinal pattern left two regions, one anterior and one posterior to the acetabulum, devoid of spines. Uniciliate papillae were found in a distinct pattern associated with the spined areas. In the pulmonary phase, the mesocercariae transformed into diplostomu- la. Earlike lappets on either side of the oral sucker developed with subsequent differentiation of microvilliform processes on their ventral sides. Body spines divided to give rise to three-pronged serrations. A depression on the venter between the acetabulum and posterior end of the body gave rise to the tribocytic organ. Stout, densely- clustered spines arose de novo on this organ. A rudimentary cylindrical hindbody gave the diplostomulum a distinct scoop-shaped appearance. Worms coughed up from the lungs and swallowed were later found in the duodenum. This postpulmonary phase of migration was a quick event and young worms in the duodenum were indistinguishable from those in the lungs. Within 4 days, the diplostomula in the duodenum matured to adult- hood. All worms in the duodenum attached to a villus by the forebody. The entire forebody of the adult appeared as a template of the host villus and this may, in part, account for the host specificity observed at the adult stage. The lappets embedded deeply into the host mucosa. Tips of body spines divided further to give rise to five- or six-pronged serrations. The tribocytic organ differentiated into a region with stout spines with an inner area of labyrinthine tegument. The hindbody grew rapidly, reflecting the maturation of the reproductive organs located there. Based on the hypothesis that migratory stages possess simple, posteriorly directed spines and nonmigratory stages possess serrate spines, we propose that the postpulmonary phase of migration in Alaria marcianae is orchestrated by the defense mechanisms of the host rather than by an active migration on the part of the diplostomulum.

Studies were made to determine whether chickens and pigeons could serve as paratenic hosts of Toxocara canis. It was found that both types of hosts harbored living infective-stage larvae for at least 142 days after inoculation. At this time, of the number of larvae inoculated, it was possible to recover approximately 30% from chickens and 18% from pigeons. Human infections with larvae of Toxocara canis are known to occur throughout the United States and in Mexico, Europe, Australia, the Philippines, and South Africa (Beaver, 1962). In the majority of cases, the infected individual is a 1to 3-year-old child who acquired the infection by ingesting infective eggs in contaminated soil (Beaver et al., 1952). In some cases, however, especially those in which the eye is invaded, the infected individual is an older child or young adult (Beaver, 1962). Although in such instances the invading larvae possibly have persisted elsewhere in the body since early childhood, it is also possible that they were acquired by eating raw or poorly cooked parts of infected meat animals. T. canis larvae persist for months or years in a wide range of mammalian laboratory hosts (Beaver, 1962), and it is presumed that they are transferred from animal to animal through paratenic hosts in nature (Sprent, 1954). It has been suspected that the eosinophilia observed in persons eating raw liver for the control of pernicious anemia was caused by infection with nematode larvae, possibly Toxocara, harbored in the liver (Beaver, 1956). Done et al. (1960) found that in the experimentally infected pig, many infective-stage Received for publication 21 August 1963. * Supported by grants EF-, EPD-14573, and AI04919 from the National Institutes of Health, U. S. Public Health Service. t Present address: Department of Veterinary Parasitology, Agricultural and Mechanical College of Texas, College Station. larvae of T. canis could be recovered from the liver, brain, lungs, and muscles more than 2 months after inoculation. In a similar study on T. canis in sheep and lambs, Schaeffler (1960) recovered the larvae from liver, muscle, and other tissues 3 months after inoculation. Studies on poultry have been brief and inconclusive. Sprent (1956) recovered six larvae of T. cati from the carcass of an experimentally infected chick at 10 days but none could be found in others at 15, 20, or 25 days. Beaver (1956) found that larvae of T. canis persisted for at least 3 months in the liver of chickens and pigeons. The present study was undertaken to get further information on the persistence and distribution of T. canis larvae in the tissues of chickens and pigeons. MATERIALS AND METHODS T. canis eggs obtained by sedimentation of feces from naturally infected dogs were incubated in 1% formalin at room temperature for 4 to 6 weeks before use. Estimated numbers of infective eggs were injected by pipette directly into the crop of young chickens and pigeons. Recovery of larvae was accomplished by two procedures: by one, the tissues were ground in saline with a Waring blendor and digested in 1% pepsin (pH 1.5) in saline (0.83%) at 37 C for 3 to 4 hr; suitable aliquots were then washed and concentrated by centrifugation in saline and the sediment was examined microscopically for larvae. By the other, tissues were chopped and finely minced with scissors and scalpel, placed in a Baermann apparatus in which the suspending medium was pepsin digest fluid, allowed to stand at 37 C for 3 to 4 hr, after which the sediment was collected and examined in the usual manner. This method, though

Twenty-three of 43 frogs (Hyla aurea) from market gardens in Noumea, New Caledonia were found to harbor infective-stage larvae of Angiostrongylus cantonenisis in their tissues. The larvae were encapsulated in the wall of the alimentary tract, the mesentery, liver, and somatic musculature; they were infective for rats. Sea snakes (Laticauda colubrina) were experimentally infected with third-stage A. cantonensis larvae and in these hosts the larvae survived and remained infective for rats for at least 1 month. The use of paratenic hosts by A. cantonensis and other metastrongyles is discussed. Very little is known as to the extent and significance of the role played by paratenic hosts in the transmission of metastrongylid infections in nature. The Hobmaiers (1935) were the first to note the use of such hosts among the metastrongyles when they demonstrated that amphibians, reptiles, birds, and mammals could serve as experimental hosts for larvae of the cat lungworm, Aelurostrongylus abstrusus. Subsequently, it has been shown that other metastrongyle larvae will enter the tissues of various vertebrates that possibly may serve as paratenic hosts in nature (Gerichter, 1949; Seneviratna, 1959; Anderson, 1962). The discovery that Angiostrongylus cantonensis, a parasite of rats, may infect man and cause eosinophilic meningitis has served to focus attention upon the biology of this nematode in particular, and upon metastrongyles in general. Thus far, infectivestage A. cantonensis larvae have been reported in nature from such paratenic hosts as planarians (Alicata, 1962), shrimp (Alicata and Brown, 1962; Rosen et al., 1967) and land crabs (Alicata, 1964b). In addition to these natural infections there have been successful experimental infections of shrimp (Wallace and Rosen, 1966), fish (Wallace and Rosen, 1967) and pigs and calves (Alicata, 1964a). Observations reported in this paper further extend the paratenic host range for A. cantonensis to amphibians and reptiles. Received for publication 16 February 1968. * Present address: Division of Infectious and Tropical Diseases, School of Public Health, UCLA, Los Angeles, California 90024. RESULTS 1. Natural infection in frogs In the course of surveying market gardens in Noumea, New Caledonia for mollusks and other invertebrates harboring nematode larvae frogs infected with A. cantonensis were found on several occasions. Hyla aurea (Less.) was the frog collected. This species was originally introduced from Australia and is the only known species of frog to occur in New Caledonia. It is relatively small, 5 to 7 cm long, and may weigh from 5 to 27 g. Examination of the stomach contents of these amphibians revealed that while insects probably comprise the bulk of their diet the remnants of mollusk shells as well as the bodies of smaller frogs were not uncommon findings. From mid-1966 to April 1967 a total of 43 frogs (29 females, 14 males) were examined for infection with A. cantonensis. In each instance, except as subsequently noted, the entire frog was examined for the presence of larvae by digestion in 0.5% pepsin in 0.7% HC1 and by pressing the tissues between thick glass slides. The frog was killed, skinned and the mesentery was examined for the presence of encapsulated larvae. Selected organs and tissues were then removed and divided into four groups for digestion: (1) alimentary tract and mesentery, (2) liver, (3) rear legs, and (4) rest of the carcass. Following digestion for 2 to 3 hr the digests were allowed to sediment in a modified Baermann funnel for an additional 2 to 3 hr prior to examination for larvae. Tissues that were examined for larvae

The author rejects the generally accepted view of the terrestrial origin of the Ascaridoidea from the Rhabditoidea by way of the Oxyuroidea, in which the direct life history is regarded as the primitive pattern of transmission. He advocates instead a marine origin and argues that the lips, esophagus, and excretory system of the ascaridoids can be equally well derived from such free-living marine forms as Enoplus, and he regards terrestrial forms as a secondary radiation. According to this view, forms having three hosts (an invertebrate paratenic host, with the second-stage larva in tissues; a small predatory vertebrate with the third-stage larva in its tissues, and a dominant predatory vertebrate harboring the fourth-stage larva and the adult) are the most primitive, and those having two and one are progressively more adaptive. The direct life history of such one-host ascaridoids as those of man, horse, and pig represent adaptations to the absence or loss of the predatory habit on the part of the host. These speculations, as well as the history of the classification of the group, are treated in detail. The starting point of this review is Chitwood's statement (Chitwood, 1950, p. 195), regarding his views on the origin of the Ascaridoidea. In essence this statement proposed that: (a) they arose from a primarily terrestrial stem, probably from the Rhabditoidea through the Oxyuroidea, (b) the marine forms arose as a secondary radiation through fish traveling up rivers from the sea, (c) that the direct (monoxenous) life-history pattern is more primitive than the indirect (heteroxenous) pattern which arose secondarily. It is probably true to say that these views were to some extent influenced by the fact that most of the previous investigations relating to the life history of the ascaridoid nematodes had been directed to the large roundworms of man and domestic animals. These findings had made such an impact on contemporary parasitologists that the direct life history was regarded as an established pattern for the whole group. This may partly explain why the indirect life-history pattern, involving one or more intermediate hosts, as demonstrated for * Dr. Sprent prepared this lecture on the occasion of his receipt of the Henry Baldwin Ward Medal. Because of its length, the address was presented as the first paper on the Symposium: The Future of Nematology, Thursday morning, 14 June 1962, at 8:30 Am. A briefer response, which will be printed later in the Journal, was made at the time of the award. marine ascaridoids by Wiilker (1929), was regarded as a secondary development. In the past 12 years there has been at least a partial change of viewpoint regarding the evolution of the ascaridoids. It is intended in this paper to outline the developments which have influenced this change. Broadly speaking, three main types of investigation have contributed: (1) elucidation of life-history patterns in individual species, (2) morphological observations on the group as a whole, and (3) discussions on the phylogenetic significance of certain morphological features and life-history patterns. In the first category we must acknowledge the contribution of Tiner (1949) who first demonstrated the role of intermediate hosts in the life history of ascaridoids of terrestrial mammals. This discovery focused attention on a number of isolated observations, which together indicated that the indirect life history is much more widespread among the group than was previously realized. Accumulation of this evidence was considerably facilitated by the publication of "The Ascaridata of Animals and Man" by Mozgovoy (1953). This two-volume compilation in Russian, besides being the first comprehensive account of the ascaridoids, included a number of observations on life histories which had been undertaken in the Soviet Union and were not hitherto readily accessible.

The experimental life cycle of Alaria (A.) marcianae (La Rue, 1917) Walton, 1949, involves planorbid snails, Helisoma trivolvis and H. campanulatum, as first intermediate hosts; tadpoles of the leopard frog, Rana pipiens, as second intermediate hosts; mice, rats, and chicks as paratenic hosts; and the domestic cat as definitive host. The life cycle is similar to known cycles in the subgenus Alaria, where avian and mammalian intermediate hosts of the mesocercariae serve as paratenic hosts; but it differs from the only known cycle in the subgenus Paralaria, where the mesocercariae develop into metacercariae in avian and mammalian intermediate hosts. This difference in mesocercarial behavior represents a distinct biological difference between members of the two subgenera and is an additional subgeneric character. Alaria (A.) minnesotae Chandler, 1954, is a synonym of A. (A.) marcianae (new synonymy). Six Alaria spp. belonging to the subgenus Alaria Schrank, 1788, have been described from indigenous North American carnivores: A. americana Hall and Wigdor, 1918; A. arisaemoides Augustine and Uribe, 1927; A. oregonensis La Rue and Barone, 1927; A. canis La Rue and Fallis, 1934; A. minnesotae Chandler, 1954; and A. marcianae (La Rue, 1917) Walton, 1949. Of the first five species, Dubois (1963) considered only A. americana and A. arisaemoides valid. Alaria marcianae, the subject of this study, was not included in his revision. From 1960 to 1964, the writer collected adults of an Alaria (A.) sp. from several different carnivore hosts in Minnesota. Additional specimens collected during 1937 and 1938 were available for study. Morphological studies were made of these worms, and the complete life history was studied in experimental hosts beginning with eggs. These parasites were then identified as A. marcianae.

Previous records of acanthocephalans in man are reviewed. Acanthocephalus bufonis (Shipley, 1903) Southwell et Macfie, 1925, is reported from man for the first time, recovered on autopsy of an Indonesian in Djakarta. Corynosoma strumosum (Rudolphi, 1802) Liihe, 1904, is reported from an Eskimo in Alaska, the first record of this parasite from man. Infections of man with acanthocephalan parasites are rare. Many species in this phylum are known to have low host specificity (Golvan, 1957) but for ecological reasons are not likely to be ingested by humans. The intermediate hosts of all species whose life cycles are known are either crustaceans, myriopods, or insects. However, several species are known to utilize fish, amphibians, or reptiles as paratenic hosts, thereby increasing the chances of accidental parasitism in persons eating such animals raw or undercooked. Lambl (1859) gave the first report of a thorny-headed worm in man when he recovered a Macracanthorhynchus hirudinaceus from a child in Prague. Lindemann (1865) stated the infection was common in Russia, where Schneider (1871) found that scarabaeid beetle grubs, the intermediate host, were commonly eaten raw. Gonzaga (1921) recovered eggs of M. hirudinaceus in two of 1,236 human stools in Brazil. A more recent case of proved chronicity was published by Pradatsundarasar and Pechranond (1965) in Thailand. Moniliformis moniliformis, a parasite of rats and cockroaches, has been reported from man in Italy, Sudan, and British Honduras (Faust and Russell, 1957), and Beck (1959) reported it from a patient in Florida. Grassi and Calandruccio (1888) reported on the symptoms displayed by the second author after voluntarily infecting himself with M. moniliformis. Kuntz (1960) reported acanthocephalan eggs, possibly those of this species, from stools of two children in Dacca, East Pakistan. Moore, Fry, and Englert (1969) made the interesting discovery of acanthocephalan eggs in human coprolites obtained in archeological excavations in Danger Cave, Utah. RadiocarReceived for publication 20 October 1970. bon dating placed the samples at 1869 BC ? 160 years, and AD 20 ? 240 years. The authors suggested that the parasite may have been Moniliformis clarki, which is common in the area. The only acanthocephalan outside the class Archiacanthocephala reported from man is A anthocephalus rauschi, recovered by Dr. Rob rt Rausch from the peritoneum of an Eskimo in Alaska, and described by Golvan (1969). The normal definitive host is probably a fish. The present paper reports the occurrence of two more palaeacanthocephalans in humans. Acanthocephalus bufonis (Shipley, 1903) Southwell et Macfie, 1925 (Syn. Acanthocephalus sinensis Van Cleave, 1937) In 1954, during a routine autopsy by Dr. Lie Kian Joe at the Medical School in Djakarta, Indonesia, four male acanthocephalans were recovered from the small intestine of an Indonesian man by screening the contents of the intestine with a metal sieve routinely used to collect hookworms. No wild animals were dissected in the autopsy room, and there was no chance that the specimens came from an outside source and had become mixed with material from human autopsies. Due to a lack of library facilities in Djakarta it was impossible to identify the worms to species; they were reported as Acanthocephalus sp. by Lie Kian Joe and Tan Kok Siang (1959). One specimen was lost prior to the present study. I now know them to be adult males of Acanthocephalus bufonis, a very common parasite of amphibians in Asia (Yuen and Fernando, 1967). Its life cycle is unknown but probably involves a terrestrial isopod crustacean as intermediate host. I can speculate that the man became infected in one of three ways: (1) by ingesting an infected arthropod; (2) by eating an am

Following the identification of the larval stage of Toxocara canis in the liver of a child in New Orleans (Beaver et al, 1952), numerous confirmatory case reports have shown that infection with larvae of this ascarid of dogs is an important cause of disease in children. Inasmuch as infection is acquired through ingesting soil previously contaminated by infected dogs, children at the dirt-eating stage of development are most frequently and heavily infected. In most of the temperate and warmer regions of the world T. canis infection in dogs is extremely common. It occurs most frequently in young dogs and is more common in the male than in the female adult (Ehrenford, 1957). It has been found prevalent among well-cared-for as well as stray dogs in New Orleans (Vaughn and Jordan, 1960). Infective eggs of T. canis have been found abundantly in door-yard soil (Headlee, 1936; Beaver, 1952). These conditions provide opportunities for young children to acquire various degrees of superinfection. Acquired resistance to nematode infection has been frequently demonstrated. As far as ascarids are concerned, the general conclusion has been that previous infection induces resistance which affects primarily the migration and survival of larvae in the tissues. Studies on the larvae of the pig ascaris have shown that fewer of them can be recovered from the liver and lungs of mice previously infected than from those given equivalent single inoculations (Wagner, 1933) ; single or multiple sublethal inoculations render guinea pigs resistant to otherwise lethal doses of infective eggs (Kerr, 1938); and in mice immunized by previous infections, the larvae are retarded in their growth and migration, remaining for longer periods in the liver before migrating to the lungs (Sprent and Chen, 1949). Comparative studies on the larval migration patterns of various ascarids have shown that Toxocara canis differs fundamentally from Ascaris lumbricoides in that its larvae are adapted to paratenic transfer, i.e., passage through a succession of intermediate cannibal or predator hosts after having reached infectivity for the final host (Sprent, 1952); therefore, the larvae of these 2 species may be affected differently by superinfection.

Various helmlinth parasites of dogs and cats are known to develop or live in man (Echinococcus spp., Toxocara spp., Dipylidium caninurm, Ancylostonma braziliense, A. caninum, Uncinaria stenocephala, and possibly Tr'ichuris vulpis) and some are capable of causing very serious pathological conditions. Of the human infections acquired through close association with dogs and cats in the United States, England, Puerto Rico, and undoubtedly other areas, perhaps next to Echinococcus the most significant, widespread, and damaging is that known as visceral larva migrans caused by the roundworn of dogs, Toxocara canis. The roundworm of the cat, T. cati, may also be of some importance in causing this disease in man. Visceral larva migrans is primarily a disease of toddleage children who ingest soil polluted with the eggs of Toxocara. Since Toxocara does not mature in man, a paratenic host, no eggs are produced for easy diagnosis. The second stage larvae may migrate through the organ systems (liver, lungs, brain, kidneys, eyes) for several weeks and remain alive encapsulated for many months, sometimes causing petit mal attacks, blindness, and even death (Beaver, 1956). Dent (1960) and Ashton (1960) indicate that eye infections have been found following mild Toxocara infections in which symptoms were not outstanding. A usual clinical finding, even in the absence of other symptoms, is eosinophilia frequently exceeding 50 percent persisting at a high level usually for a year or more, but which may be absent in eye infections.

Larvae of the dog hookworm, Ancylostoma caninum, can invade and remain infective for more than 1 year in the tissues of various rodents (Nichols, 1956). As these larvae can infect cats and dogs by mouth as well as by skin, it is possible that infected rodents may serve as natural paratenic hosts. The purpose of the present study was to determine whether insects may serve as paratenic hosts in the same manner. Cockroaches were chosen for investigation because they are commonly eaten by cats, they are likely to be in contact with hookworm larvae under natural conditions, and they have been suggested as natural paratenic hosts for other nematode parasites of cats (Sprent, 1956).