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Specimens of Acrotelsa collaris were confined on representative paper samples and on filter paper impregnated with milk food. Each stadium was divisible into a feeding and a non-feeding period. Stadial and feeding durations (42 ± 1 and 29 ± 1 days) were not statistically different on the untreated papers except one. On the milk food paper stadial and feeding durations were significantly shorter (27 ± 2 and 18 ± 2 days). However non-feeding periods were not significantly different (12·0 ± 0·5 days). The total amounts of the different papers ingested in a single feeding period were similar. Art and milk food paper were eaten faster. The approximate digestibility values were in the range 63–77 per cent. There was a general loss in body weight, except on milk food paper that was replaced periodically.

Under optimal conditions, adult firebrats moult about every 9 days (English strain) or 13 days (American strain), irrespective of age, sex, or reproductive activity. The epidermis is activated on the 4th or 5th day of the 9-day stadium and the deposition of the cuticle follows 2 days later. There is a critical period for the secretion of a brain hormone on the 5th or 6th day of a 13-day stadium, equivalent to the 3rd or 4th day of the 9-day stadium; maximal activity in the ventral gland coincides with or follows shortly after this, also coinciding with the activation of the epidermis. Thus the control of moulting in Thermobia closely resembles that in the pterygotes.

The female firebrat can mate from the first to the fifth day after ecdysis, but most mate between the first and third days. Mating initiates the deposition of proteinaceous yolk in the oocytes, oviposition following 2–4 days after mating. Thus, on the average, 4·69 days elapse between ecdysis and oviposition, with a standard error of 0·13 days, so that oviposition occurs almost exactly half-way through each adult stadium. The male also mates most actively during the first third of the stadium if exposed continuously to females, but the potential for full mating activity persists into the seventh day of the 9 day stadium in celibate males. The difference appears to depend on a finite capacity to produce spermatophores in any given stadium. As a result of these restricted mating periods, isolated pairs of firebrats can reproduce only if male and female moult within 3 or occasionally 4 days of each other.

The ultrastructure of the epithelial cells of the vasa efferentia, vasa deferentia and the seminal vesicle of Thermobia domestica is described. Some of the striking features of the epithelial cells of the vas efferens are the displacement of most of the cytoplasm along the cell periphery, resulting in the appearance of intracellular spaces; an unusual arrangement of the endoplasmic reticulum, the deflection of the outer nuclear membrane deeper in the cell so as to enclose the cytoplasmic organelles. The epithelial cells of vas deferens display prominent infoldings of the plasma membrane, an elaborate rough endoplasmic reticulum, and numerous electron dense secretory bodies interspersed in the cytoplasm. The seminal vesicle with thick striated muscular wall acts as a store for the mature spermatozoa.

TRICHOLEPIDION gertschi was found under decaying hark and in rotten logs of Douglas-fir in the mesophytic forest of the northern California Coast Range. It is closely related to the Baltic amber Lepidothrix pilifera Menge, differing mainly by the presence of ocelli. T. gertschi (and, by implication, also L. pilifera ), compared to the remaining Thysanura (families Nicoletiidae and Lepismatidae), is characterized by a large number of primitive characters, such as lack of scales, combined with presence of hypodermal pigment; the hypognathous head with exceptionally well developed occipital and postoccipital sclerites; the presence of three pectinate appendages to the laciniae; weakly developed thoracic sternal plates; a large number of abdominal stylets and exsertile vesicles; urosternites composed of a large, transverse sternite and posteriorly situated coxopodites, both elements being well developed even on the eighth and ninth segments of the male; the lack of a proventriculus; and the presence of seven ovarioles in each ovary. Specialized characters probably shared by both genera of Lepidotrichidae are the five-segmented tarsi; the modified ovipositor adapted to insertion of eggs into vegetable tissue; a group of specialized setae on the dorsal surface of the base of the penis; a very large number of testicular follicles; and forwardly directed diverticula of the vasa deferentia functioning as sperm reservoirs. Pairing of mature sperms in Tricholepidion is considered as a condition precursory to the development of spermatophores as observed in the Nicoletiidae; the presence of sensory cones on the underside of the median caudal filament in the males is equally indicative of relationship with the Nicoletiidae. The Lepidotrichidae are considered to be the most archaic known dicondylous insects ; their relic character is further stressed by their actual geographic distribution.

Since the end of the Nineteenth Century the taxonomy of the small order Thysanura has been extensively treated by a few specialists, notably F. Silvestri, P. W. Wygodzinsky, and to a lesser degree K. W. Verhoeff, K. Escherich, H. W. Womersley, and J. Stach. All of these men have recognized and named various new genera and numerous new species. Among them only Verhoeff and Escherich have attempted to develop a major classification of the species into supra-generic groups. Verhoeff's classification of the saltatorial Thysanura (Machilidae of most textbooks) and that of Escherich for the non-saltatorial forms (Lepismatidae of authors) are still followed with little change by recent students of the order.

The several organ systems of these two species are described, compared, and illustrated. Differences were found in the tracheation of the eye, the disposition of vestigial stylal tracheae, and the absence in L. saccharinum of the ventral tracheal commissure of the eighth abdominal segment. The digestive system follows a generalized plan, similar to that of Orthoptera. In C. campbelli , but not in L. saccharinum , the first five abdominal ganglia have migrated one segment forward, but each continues to innervate the segment from which it came, whether a tracheal connection with that segment is preserved or not; the different behavior of tracheae and nerves in relation to such migrated ganglia seems a result of the sequence of their formation in the embryo. In both species the dorsal vessel is pulsatile for its whole length, but little or no peristalsis was observed; instead, systoles occur alternately in an anterior and a posterior chamber which are separated by a thoracic valve. Ten pairs of ostia were observed with difficulty through the transparent integument of living C. campbelli; probably those of L. saccharinum are similar. Pericardial cells were less numerous in the former than in the latter species. Each ovary consists of five ovarioles, connected to a common duct near the base of the ovipositor; the spermatheca lies beneath the eighth abdominal ganglion and communicates with the oviduct, ovipositor, and genital pore above the eighth sternite. Males have three pairs of testes on each side of the body, each pair discharging through a common vas efferens into a vas deferens which leads to one of the two seminal vesicles; and from this a long tube, with accessory glands apparently built into it, runs to the base of the acdeagus. Apical cells, not previously known in Thysanura, were found present in the testes. Histological sections of the aedeagus and its base provide, for the first time, evidence for a paired origin of this organ in Apterygota.

Six types of sense organs are present on the antennal flagellum of Ctenolepisma lineata pilifera: tactile hairs, trichobothria, thick-walled chemoreceptors, small thin-walled chemoreceptors and coeloconic chemoreceptors. The number, size and distribution on the antenna of each type have been recorded. The base of the tactile hair is more complex than is that of other insects examined earlier. Trichobothria, long, slender hairs that oscillate in a gentle puff of air, are an unusal feature in insects and especially so for the antenna. The two types of thin-walled chemoreceptors differ in shape, size and in the structure of their walls and internal parts. A pocket-like depression of the floor of the cavity in which the peg of the coeloconic sense organ is set has not been found in earlier studies. Its function is unknown. The axons from the sensory neurons extend along the inner surface of the antennal epidermis as a sheet of fibers lining the antennal lumen. Near the pedicel the axons leave the epidermis and join to form the antennal nerve. A few observations on sense organs on appendages other than the antennae and some notes on behavior are included.

Under optimal conditions, reproduction does not affect the rate of growth in female Lepisodes. In unmated male and female firebrats, an increase of weight after ecdysis is associated with a single phase of feeding activity, which terminates near the middle of the instar, coincident with the reconstruction of the midgut epithelium. In mated females, a greater increase in weight accompanies a more intense first phase of feeding, and at oviposition a short second phase of feeding commences. The weight of food consumed in this second phase is closely correlated with the weight of eggs laid, and evidently compensates for loss of reserves at oviposition.

The morphology and histology of the different regions in the alimentary canal of Lepisma saccharina are shortly described. The regular occurrence of one type of bacterium and two species of eugregarines is reported.

The reduction of the Strepsiptera to a family of Coleoptera in a recent textbook on beetles of the United States is found untenable. The Strepsiptera have a unique hypermetamorphic development, carried on entirely in the bodies of other insects of the orders Zygentoma (Lepismatidae), Orthoptera, Homoptera, and Hymenoptera. The female of Eoxenos (a parasite of Lepisma ) redevelops legs and emerges from the host to free her young; in all other members of the order the females are legless sacs, with cephalothoracic plates protruding from the host abdomen to receive sperm from the male and to permit exit of the active first larvae. Males all are winged, and are separated into families and super-families on the bases of reduction of tarsal joints, antennal joints, and wing veins; the tarsi are isomerous, never heteromerous as in the Coleoptera to which Strepsiptera have been referred. Pupal development of the males with a puparium with detachable cephalotheca does not occur in Coleoptera, but is found in Strepsiptera, Aleurodoptera, Coccoptera, and cyclorrhaphous Diptera. Free first larvae also occur in other orders, and do not constitute a valid character for uniting Strepsiptera with Coleoptera. The strepsipterous metathorax has the same parts as in the Aleurodoptera, and is totally unlike the coleopterous thorax. The simple wing venation is distinctive; the mouthparts are nonfunctional and very distinct from those of Coleoptera; the raspberrylike compound eyes are similar to those of Coccoptera, some Diptera, and a few other groups, but not like those of Coleoptera.

Lepisma [gen. nov.] Pedes VI, cursorii. Os Palpis II. Cauda setosa: setis extensis. Corpus squamis imbricatum., Published as part of Linnaeus, Carolus, 1758, Systema Naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis, Stockholm :Laurentius Salvius on page 608, DOI: 10.5962/bhl.title.542, http://zenodo.org/record/3922206

Lepisma saccharina [spec. nov.] L. squamosa, cauda triplici. Brown. jam. 425. Setoura subargentea, cauda setosa, setis hirsutis. Adam. microgr. t. 28. f 147. Habitat in America inter saccharum & utensilia domestica, inde per Europam vulgaris, hodie in S{?X} incepit., Published as part of Linnaeus, Carolus, 1758, Systema Naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis, Stockholm :Laurentius Salvius on page 608, DOI: 10.5962/bhl.title.542, http://zenodo.org/record/3922206

Lepisma terrestris [spec. nov.] L. nuda, cauda triplici. Habitat in Europa. Similis Podurae sed major, corpore toto albo cylindrico, Antennae corporis dimidii longitudine, obtusae ut in Podura., Published as part of Linnaeus, Carolus, 1758, Systema Naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis, Stockholm :Laurentius Salvius on page 608, DOI: 10.5962/bhl.title.542, http://zenodo.org/record/3922206