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The metacercarial stage of Gymnophalloides tokiensis has a mid-ventral pit which was mistaken in the original description for a wide genital pore. The genital pore is small, on the anterior edge of the ventral sucker, and not surrounded by prominent muscle fibers. Other corrections of the original description include paired, compact vitellaria (referred to as Mehlis gland), a bipartite (not globular) seminal vesicle, and an ovary smaller than the testes; no eye spots or a seminal receptacle are present.Yamaguti's (1971) synonymy of Lacunovermis Ching, 1965 with Gymnophalloides is rejected because of the differences in the location and type of genital pore. In contrast to G. tokiensis, both L. conspicuus and L. macomae (Lebour, 1908) Loos-Frank, 1970 have a wide genital pore that opens some distance from the ventral sucker and both ventral pit and genital pore are surrounded by strong muscle fibers.Two of Yamaguti's (1971) footnotes about gymnophallid trematodes are corrected. In my 1965 paper, I did not synonymize Gymnophalloides with Meiogymnophallus but replaced Gymnophalloides as emended by James (1964) with the name Meiogymnophallus. I did not synonymize Gymnophallus oidemiae, now M. minutus (Cobbold, 1859) Bowers and James, 1967, with G. somateriae but regard them as distinct species.

Evidence obtained would suggest that the processes involved in egg formation in Fasciola hepatica occur in the following sequence. The egg constituents, namely an ovum and some vitelline cells, pass through the proximal ootype and as they do so they are smeared by the secretions of Mehlis' gland which have accumulated there. A temporary interface is set up between the Mehlis' gland secretion and the fluid which surrounds the egg constituents. Shell globules are released by the vitelline cells and coalesce on the inner aspect of the interface. At the same time some of the Mehlis' secretion diffuses across the interface, thereby bringing about the dissociation of the interface. It is suggested that Mehlis' gland secretion brings about the fusion of the shell layer. During the initial stages of the process the developing egg is supported by the cells of the ootype epithelium. Later the egg passes into a wider, more distal part of the ootype where the process of shell deposition is continued. When complete, or almost complete, the egg passes into the uterus where changes indiciating the initial process of tanning are seen to take place. A thin, very uniform layer of Mehlis' gland secretion can still be identified on the surface of mature eggs.

The oogenotop was studied using certain histochemical tests and the contributions of the various parts to the egg were noted. The Mehlis gland and the uterine epithelium make large contributions to the egg. Both the inner and outer envelopes are of reduced importance. A photographic record of oogenesis is presented showing it follows previous descriptions for the Cestoda. The first cleavage is unequal. Shell granules from the oocyte are carried to the macromeres where they are used in the formation of the outer capsule. Hatching is standard for eggs with a membraneous inner capsule. Most infections are characterized by one female and one male worm. Microsporidians reduce the number of sperm produced and probably limit the production of oncospheres.

1. 1. When exposed in vitro to C 14 proline male schistosoma become much more heavily than do females. 2. 2. The areas of concentration in the male are the integument and sub-integument, the paraoesophageal region, the gut and the testes. 3. 3. In the female local accumulation in the posterior ovary and, to a lesser extent, in the mehlis gland was noted. 4. 4. The vitelline gland and duct fail to tag heavily on exposure; the female gut also shows minimal proline uptake. 5. 5. Proline may play a special metabolic role in either the paraoesophageal musculature or in the nearby neural ganglionic ring. 6. 6. Speculations concerning functional implications of these findings are given.

Mehlis' gland of F. hepatica is composed of two secretory cell types supported by parenchymal cells. The products of the secretory cells are carried by means of cytoplasmic extensions into the ootype. The most prevalent type of secretory cell is termed S 1 type. It possesses many narrow granular endoplasmic cisternae and numerous Golgi complexes. The secretory bodies of this cell resemble slightly curved sausages and have a filamentous content radiating from a central core. The other secretory cell type is termed S2 type. It is characterized by distended granular endoplasmic cisternae and numerous Golgi complexes which give rise to round dense secretory bodies with a crystalline or packed fibrous appearance. Both types of secretory cells are penetrated deeply by invaginations of interstitial material. The cytoplasmic extensions from the cells are lined with microtubules and anchored to the epithelial cells lining the ootype by septate desmosomes. The secretory bodies of both cell types are released into the lumen of the ootype, where they disintegrate.

Histochemische Untersuchungen der Mehlischen Druse vonFasciola hepatica erweisen deren Phospholipidabsonderung. Es wird auf die Moglichkeit einer engen Bezichung des Phospholipids zu Lezithin und seine enzymatische Aktivierung zur Herauslosung von Eischalenprokursoren hingewiesen.

The cells of Mehlis's gland in the liver fluke (Fasciola hepatica L.) have been studied with light and electron microscopy. The gland contained large cells in the periphery and small cells in the centre. The large cells presented morphological features characteristic of secretory cells, viz. large nucleoli, cytoplasmic basophilia, a well developed endoplasmic reticulum, abundant ribosomes, and secretory granules in different stages of development. The mitochondria were moderately frequent. Several small groups of vesicles and membraneous lamellae reminiscent of Golgi complexes occurred randomly in the cytoplasm. These structures were associated with mitochondria and secretory granules. Evidence of alterations and conversion into a cell debris was observed, and a process of holocrine secretion was suggested.

reproductive system of the trematodes and cestodes, and consists of a series of glandular structures surrounding the ootype, the tube connecting the oviduct to the uterus. These glands vary in number and arrangement in the different groups and species. This gland is particularly well developed in the liver fluke, F. hepatica, where its huge size has made it difficult to appreciate its relationship with the complicated system of ducts embedded in it. In consequence there has been a conflict in interpretation (Stephenson, 1947, Yosufzai, 1953) and the purpose of this paper has been to attempt some clarification.

Egg shell formation for Parastrigea mexicanus is described. Eleven histochemical tests were used to elucidate the process and to characterize the oogenotop. The egg is formed in the ootype (a region of high secretory activity); an oocyte and 12-17 vitelline cells are enclosed by a coalescence of vitelline shell globules. The vitelline cells also contribute copious amounts of glycogen and RNA. There was no direct histochemical evidence for Mehlis or uterine gland function; however, secretory functions were inferred from morphology and histochemical reactions. The basic mechanism of egg shell formation in P. mexicanus closely follows that of Fasciola, but it differs in some regards from the process described for the latter trematode. Helminthologists have studied egg shell formation in trematodes for 82 years now and their efforts have concentrated on widely separated taxa. In spite of this long period of time and the many investigators involved, only a few of the more than 100 families of digenetic trematodes have been studied in this regard. Our approach has been a comparative one and to date, we have completed studies on representatives from the following families: Fellodistomidae, Hasstilesiidae, Hemiuridae, Microphallidae, Notocotylidae, Pronocephalidae, and Syncoelidae. Fasciola hepatica has received the greatest attention; Haematoloechus has been studied in some detail also. Egg shell formation in the digenetic trematodes appears to follow a generalized mechanism which has been elucidated by a number of authors and reviewed by Smyth & Clegg (1959). Since that date, a number of papers have described variations on the central theme. Recently, Ebrahimzadeh (1966) studied 27 species (from ten families) on a comparative basis and he thus established a standard of excellence for students of egg shell formation to follow. During the course of other studies on parasites of the black-necked stilt, the author collected a large number of Parastrigea mexicanus Coil, 1955 (Strigeidae). Although the strigeoids have received much attention concerning their life cycles, it has been only recently that details of their morphology have been studied; many of these have emphasized the holdfast organ (Erasmus, 1968; and others). There are certain striking features of these worms which warrant further studythe large amount of tissue devoted to vitelline production, the extensive Mehlis gland tissue, the extremely large egg, and the nature of the uterus. P. mexicanus provides excellent material for study. The worm is short, compact, and easily handled; sectioned material can be prepared without difficulty. Microdissections are difficult, however, due to the muscular body wall and the heavy cuticle. This is the fifth report in our series of comparative studies on egg shell formation in digenetic trematodes. 1This investigation was supported by Public Health Service Grants AI 05145 and GM 12587. 2The author is indebted to Dr. Clarence Cottam and Mr. Caleb Glazener, both of the Welder Wildlife Foundation, for their help in providing facilities, equipment, and supplies for the early parts of this study. TRANS. AMER. MICROSC. Soc. 88(1): 127-135. 1969. This content downloaded from 207.46.13.21 on Tue, 27 Sep 2016 05:13:10 UTC All use subject to http://about.jstor.org/terms 128 TRANS. AMER. MICROSC. SOC., VOL. 88, NO. 1, JANUARY 1969

Observations on the functional anatomy of the ducts associated with Mehlis' gland were made in five species of echinostomes: Echinostoma malayanum, E. lindoense, E. audyi, Hypoderaeum dingeri, and a 43-spined, undescribed Echinoparyphium species. In all five species the structure of the Mehlis' gland complex is similar. There is an ovicapt in the form of a chamber which regulates the passage of the ova from the ovary into the oviduct. Ciliated epithelium lines the ovicapt, the oviduct distal to the ovicapt, and the proximal part of Laurer's canal. The movement of the cilia is directed toward Laurer's canal from which excess sperm and vitelline granules are discharged at the dorsal surface. Spermatozoa are stored in the uterine seminal receptacle in the absence of a seminal receptacle. The Mehlis' gland complex of echinostomes is best studied in living worms because the ducts and organs associated with it are not clearly visible in mounted specimens. Moreover, the gland region is often filled with eggs, making a detailed study extremely difficult or impossible. Descriptions are often incomplete and sometimes inaccurate. This paper reports observations on the Mehlis' gland complex in living specimens of five species (three genera) of echinostomes. MATERIALS AND METHODS The following species of echinostomes were studied: Echinostoma nmalayanum Leiper, 1911; E. lindoense Sandground and Bonne, 1940; E. audyi Lie and Umathevy, 1965; Hypoderaeum dingeri Lie, 1964; and an undescribed 43-spined Echinoparyphium species which will be named later when its complete life cycle is described. An unlimited supply of living worms was maintained in the laboratory for life-cycle studies. E. malayanum was obtained from rats, the other four species from pigeons and ducklings. Young adult worms with few eggs in the uterus were preferred. The Echinoparyphium species is the easiest to study since the worm is small and seldom contains many eggs; H. dingeri is the most difficult to examine due to thickness of the worm and density of Mehlis' gland. The living worm is examined dorsal side up in a drop of physiological saline under a cover slip. Received for publication 12 August 1964. * This work was supported by the University of California International Center for Medical Research and Training (The Hooper Foundation, San Francisco School of Medicine) with Research Grant GM-11329 from the Office of International Research, NIH, U. S. Public Health Service. t Present address: Hooper Foundation, University of California Medical Center, San Francisco. When movement of the worm is restricted and the position is suitable, ducts and organs in the Mehlis' gland region can be seen. An oil-immersion lens is required for detailed observation of certain parts.