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The lockdowns that came with policies to reduce the spread of COVID-19 in 2020 required some 90% of museums and historic properties across the globe to be closed. Lowered visitor numbers and reduced staffing levels allowed a range of fauna to make their way indoors, bringing an increase in birds, rodents and insect pests. Silverfish are shy, so benefit from low occupancy in museums and present a potential vector for damage to books and paper. This study is the first to report changes in insect populations in museums and examines six years (2015–2020) trapping data for silverfish and similar insects (Lepismatidae): Lepisma saccharinum, Ctenolepisma calvum, Ctenolepisma longicaudatum and Ctenolepisma lineatum from: (i) the Technisches Museum Wien, (ii) Schonbrunn Palace, (iii) Hofburg Museum and a shorter record from (iv) Weltmuseum Wien. Analysis of the trap contents gives an impression that the number of insects caught had increased over time, but 2020 was distinctive and gave typically higher insect numbers during the COVID-19 lockdown compared to other years, especially for Lepisma saccharinum. Individual traps caught up to 100 silverfish in only a few weeks. Because silverfish usually need between four months to one year to become mature, we assume that it was increased activity during museum closure and not higher reproduction which led to higher numbers. The parts of the museums showing increased populations under lockdown were similar to the areas where they were more frequent in earlier years. This means that such areas deserve continued monitoring even when the museum is closed. No damage to paper objects were reported in the museums investigated.

Two fossil silverfish preserved in Burmese amber (dated from the Cretaceous: Upper Albian, 100–110 MY) are described in the new genus and species Burmalepisma cretacicum (Lepismatidae: Lepismatinae). The fossil species is characterized mainly by its chaetotaxy.

In this study, we report the analysis of the immune-related transcriptome from an apterygote insect, the firebrat Thermobia domestica (Zygentoma, Lepismatidae), which currently emerges as a suitable model insect for evolutionary and developmental studies. The suppression subtractive hybridization method was used for targeted screening of genes that are up-regulated in response to injected bacterial lipopolysaccharide (LPS). A subtracted cDNA library enriched in immune-inducible genes was constructed and analysis of 288 cDNAs resulted in identification of 26 novel genes in T. domestica. Among these immune-related transcripts we found homologues of genes from other insects which are involved in the regulation of signaling cascades and six novel putative antimicrobial peptides. The identified genes implicate the presence of sophisticated regulatory mechanisms in insect immune signaling and give insight into evolutionarily conserved features of insect innate immunity.

Development and fate of embryonic membranes in the silverfish Lepisma saccharina was examined throughout embryogenesis. The amnioserosal folds first arise as serosal folds that are completed by the later addition of the amnion from the embryo's margins as in archaeognaths. The close link between production of the amnion and formation of the folds should not be assigned to Dicondylia but to Pterygota as an autapomorphy. During fold formation, folding of embryonic membranes beneath the embryo is less extensive and the ventral cupping of the embryo plays a larger role comparable to that occurring in archaeognath embryos. In L. saccharina, the embryonic membrane pore (the amniopore) varies in its manner of closure, either by complete fusion of serosal folds or by formation of a serosal cuticular plug between them as in archaeognaths. Although, in many aspects of its embryogenesis, L. saccharina retains the primitiveness of archaeognaths, its amnioserosal folds persist and are well integrated into its embryogenesis as the amnioserosal fold-amniotic cavity system is established and as occurs in many pterygote embryos; this may be thus regarded as an autapomorphy of Dicondylia.

Detecting the presence of active insects in various stages of their lifecycle within an art object is often difficult in the absence of direct visualization of the insect. It usually relies on one's ability to assess the evidence of their activity around, on, or in the object. To augment this “eyeball” method, a Fourier transform infrared spectroscopy system was used to determine the presence of the insect through its respired gas, carbon dioxide. The application of the procedure to assist in control of insect infestation within art objects is described. Two instruments are discussed in this paper. The prototype instrument could detect a change in carbon dioxide that was 0.3–0.4 ppm/h and required days to reliably determine this level. The second instrument could detect changes as low as 0.09 ppm/h and could provide results in only 4 h. Carbon dioxide measurements were collected from representative insect groups that have caused problems in art objects; these were worker termites ( Reticuliterme s sp.), carpet beetle adult and larvae ( Anthrenus sp.), an odd beetle larva ( Thylodrias sp.) and a mature silverfish ( Lepisma sp.), as well as selected museum art objects composed of wood, fabric, and/or feathers suspected of harboring insects.

Summary Some features of the distribution pattern of the antennal asteriform sensilla are described for two groups of Lepismatidae: Neoasterolepisma and Tricholepisma. Seventeen Spanish species have been studied, fifteen belonging to Neoasterolepisma and two to Tricholepisma. Reliable characteristics for distinguishing species are listed for the identification of males, females and juveniles. The distal part of the antenna has several annuli, wich are often arranged in groups of two, three or more units or elements; these groups of joints are called distal chains. These distal chains have been grouped two by two using the presence of trichobothria. We have verified that the number of sensilla arranged in the distal and basal annuli of each group of two distal chains is constant, as well as the number of sensilla arranged by pairs in a single annulus. Six different patterns have been found, two of them showing pairs of sensilla.

Summary The fauna of Zygentoma from Italy is reviewed and extended by new data. Ctenolepisma guadianica and Allacrotelsa kraepelini are new to Italy (the second one is also a new genus for this country). Neoasterolepisma crassipes is new to continental Italy and Atelura formicaria is new to Sicily. Neoasterolepisma angustothoracica (Grassi & Rovelli, 1890) n. comb., is redescribed. The Zygentoma fauna of Italy is composed of 24 species, 2 of Ateluridae ( Atelura formicaria and Proatelurina pseudolepisma ), 16 of Lepismatidae ( Allacrotelsa kraepelini, Ctenolepisma algharbica, C. ciliata, C. guadianica, C. lineata, C. longicaudata, C. targionii, Lepisma chlorosoma, L. saccharina, Neoasterolepisma angustothoracica, N. balcanica, N. crassipes, N. wasmanni, Thermobia domestica, Tricholepisma aurea and T. gyriniformis ) and 6 of Nicoletiidae ( Coletinia maggi, C. setosula, C. subterranea, Coletinia sp. III, Lepidospora sp. and Nicoletia phytophila ). A key to the identification of all these species is given.

Comparative morphological studies of the different types of sensilla basiconica of Lepisma saccharina (Zygentoma: Lepismatidae) and Machilis sp. (Archaeognatha: Machilidae) revealed 3 types in Machilis (sensillum basiconicum types A–C) and 4 types in Lepisma (sensillum basiconicum types D–G). No-pore sensilla (sensillum basiconicum types A, B and D) were found in both species. The organization plan corresponds to that of no-pore sensilla of pterygotan insects. Original characters are doubled basal bodies and a larger number of sense cells. L. saccharina possesses both single-walled (sensillum basiconicum types F and G) and double-walled sensilla (sensillum basiconicum type E). Machilis possesses only single-walled sensilla (sensillum basiconicum type C). For the first time a double-walled sensillum is described in apterygotan insects. The sensillum basiconicum type E is a typical double-walled sensillum but with only one circle of spoke canals near the tip of the hair shaft. A sensillum with spoke canals, but with a single wall, is also found in L. saccharina (sensillum basiconicum type G). The organization plan of the multiporous sensilla with pore tubules of Lepisma and Machilis corresponds to that of the multiporous sensilla of pterygotan insects. Sensillum basiconicum type F of Lepisma shows a peculiarity in that it is a “doubled sensillum”. All sensilla basiconica described in both Lepisma and Machilis have 4 enveloping cells and the position of the moulting porus is at the tip of the hair shaft.

Phospholipase A2 (PLA2) activity was tested in the seminal receptacle of the firebrat female during an ovarian cycle and in relation to insemination. The PLA2 activity was weak up to the time of insemination, while a strong increase of the enzyme activity occurred at the end of the ovarian cycle in both inseminated and non-inseminated females, indicating that PLA2 is an endogenous enzyme not transferred by the spermatophore. Females received various drugs whose anti-PLA2 effects were checked on the seminal receptacle tissues. The effects of the drugs were investigated on ovarian maturation and on the number of eggs layed by inseminated females. Dose-response relationships provide crucial indications that PLA2 inhibition interferes with the firebrat fecundity. The emergent picture is that oocyte maturation is insensitive to PLA2 activity, but that the treatments which reduce the release of arachidonic acid from cellular phospholipids interrupt some physiological link leading to egg deposition. The arachidonate metabolites are designated as the primer of the ovulation mechanisms; the possible role of development hormones in PLA2 regulation is discussed.

1. 1. In the primitive insect, Thermobia domestica , the two sex-specific proteins of the female are generated by both the fat body and the ovaries. 2. 2. Production from both origins was studied along an ovarian cycle and in relation to the moulting cycle. Data designate the ovaries as the highly preponderant source of yolk proteins, but only the fat body metabolism appears clearly stimulated after insemination. 3. 3. In the ovaries, the early yolk protein synthesis and its high specific activity from the onset of a reproductive cycle indicate early translation and gene amplification necessary to support the massive endogenous production.

1. 1. A variety of different digestive proteinases from the gut of the firebrat Thermobia domestica (Thysanura: Lepismatidae) was partially purified and characterized by electrophoretic methods. 2. 2. The proteolytic enzymes could be identified as a trypsin-like proteinase with a pI of 4.95 and two charge isomer cysteine proteinases with a pI of 3.5 and 3.7. 3. 3. The hydrolytic activity of the trypsin-like proteinase is optimal at pH 9.0, the cysteine proteinases have optimal activity at pH 6.0. 4. 4. The M r , was estimated by isomer analysis to be 21,000 for the trypsin-like proteinase and 42,000 for the cysteine proteinases.

Upon in vitro incubation with [ 14 ]arachidonic acid, reproductive tissues of Thermobia domestica incorporated radioactivity, mostly into phospholipids. Stimulation with calcium ionophore A 23187 modified the distribution of the labeling between the various phospholipids, and promoted a release of arachidonic acid as well as metabolites comigrating with authentic HETEs. The lipolytic activity was tested against three exogenous phosphatidylcholines. It is concluded that arachidonic acid availability for eicosanoid biosynthesis is mostly regulated by a calcium-dependent phospholipase A 2 . The specific activity of PLA 2 was assayed in reproductive tissues. After insemination, the phospholipase activity strongly increased in the female seminal receptacle, but the rise was independent of the number of transfered spermatophores.

The reproductive tissues of the primitive insect Thermobia domestica synthesize several eicosanoids when incubated with exogenous arachidonic acid. The enzymatic system was characterized with respect to kinetic parameters, Ca 2+ requirement and pH- and cofactor-dependence. Five monohydroxylated eicosatetraenoic acids (HETEs) were identified by mass spectrometry procedures, demonstrating the existence of the lipoxygenase pathway. Quantitative studies were performed by high-pressure liquid chromatography. It is confirmed that the 8-lipoxygenase activity remains the major pathway in tissues from males and from inseminated females. In female tissues, the amounts of metabolite depend on the number of spermatophores contained in the seminal receptacles. These data are in agreement with the hypothesis of a transfer of the enzyme from male to female during mating. The mechanisms involved are discussed in comparison with those of other insect species in which the synthesis of prostaglandins has been reported.

The exocrine glands located in the penis of Thermobia domestica (Thysanura : Lepismatidae) are composed of about 100 distinct units, each containing several cell types: one large secretory cell with an apical reservoir; 2 groups of envelope cells, an inner group of 2 superimposed cells, and an outer group of 4 cells arranged in a ring, and also 2 basal cells, called ciliary cells owing to their elongated processes, which look like the dendrite of a sensory cell. Each functional unit includes cuticular differentiations: a tubular bristle, fixed on a small tubercle; and a long “internal” ductule communicating basally with the reservoir of the glandular cell and opening distally at the tip of the bristle. A study of the modifications affecting the phallic glands during moulting, shows that the inner envelope cells deposit the cuticle that forms the ductule, the outer envelope cells elaborate the cuticule of the tubercle, while a temporary distal projection of only one of these cells ensures the formation of the bristle. In addition, a lengthening of the outer dendritic segment of the 2 ciliary cells takes place before ductule formation, but this segment partially degenerates after ecdysis. These findings are compared with data already obtained on the morphogenesis of other insect integumental glands. In T. domestica, the secretion of the phallic glands is presumed to be used, during the mating sequences, for spinning fine threads before spermatophore deposition.

During the moulting and reproductive cycles, which coexist in adult females of the primitive insect Thermobia domestica , the corpora allata (CA) undergo periodical changes: their volumes and numbers of cells are lower at the beginning and at the end of each moulting cycle, and higher about the middle. However, the nucleo-cytoplasmic ratio does not undergo significant variations. An ultrastructural description of the CA cells is given for the first time in a lepismatid. The glandular cells, which are all similar, undergo 2 different stages: the so-called “clear cells” present at the beginning and the end of the moulting cycle, and the “dense cells” in the middle of the cycle. If there is no insemination at the beginning of each intermoulting period, the terminal oocytes are totally resorbed and most of the CA cells are in an intermediate stage between clear and dense cells. These data are discussed in relation to the probable variations in the physiological activity of the CA during normal adult cycles.

In order to extend our knowledge of the neurohaemal organs in apterygote insects, a comparative description of the fine structure of these organs and of the aorta is given in 2 species: Thermobia domestica (Packard) (Thysanura : Lepismatidae) and Trigoniophthalmus alternatus (Silv.) (Microcoryphia : Machilidae), which are representative of the 2 now separated orders in the Thysanura (s.1.). In both species, the cephalic neurohaemal organs are formed by a pair of swellings of the aortic nerves, containing numerous axon terminals filled with neurosecretory (NS) granules, but only the NS axons of Thermobia are enveloped with glial cells. The NS products, which are not exactly similar in the 2 species, can be released into the aortic cavity. In addition, the lepismatids possess a pair of corpora cardiaca with intrinsic secretory cells, situated in the path of the cardiac nerves, close to the brain. In machilids, such endocrine organs do not exist, but a median organ—the infra-aortic corpus—also containing endocrine cells, is found in contact with the ventral aorta and connected, on each side, with the tritocerebral lobes. These observations on the neurohaemal systems agree with the concept that the machilids form a primitive group, distinctly separated from the lepismatids, which have many anatomical characteristics similar to those of lower pterygote insects.

1. 1. Cellulose digestion has been demonstrated in the Thysanura (Lepismatidae), Orthoptera (Cryptocercidae, Blattidae). Isoptera (Mastotermitidae. Kalotermitidae. Hodotermitidae, Rhinotermitdae, Termitidae). Coleoptera (Buprestidae. Anobiidae, Scarabaeidae, Cerambycidae), and Hymenoptera (Siricidae). 2. 2. In all but the scarab beetles, cellulose digestion is brought about by a complex of three types of enzymes (C1-cellulases, Cx-cellulases, and cellobiases), as in fungi. 3. 3. Many insects are able to synthesize their own Cx-cellulases and cellobiases, but few (if any) can synthesize C1-cellulases. 4. 4. Insects compensate for their inability to synthesize C1-cellulases by exploiting the cellulolytic potential of protozoa, bacteria, or fungi. 5. 5. The maintenance of permanent populations of hindgut protozoa, the maintenance of permanent populations of hindgut bacteria, and the ingestion of fungal cellulases are described as three distinct mechanisms by which insects have been shown to use the cellulolytic potential of microorganisms. 6. 6. A process in which ingested cellulolytic bacteria proliferate in one region of the gut at the expense of ingested cellulose, only to be digested and assimilated in a more posterior section, is a fourth possible mechanism by which insects might accomplish the digestion of cellulose with the help of microorganisms.

The sensitivity of an apterygote insect to precocene II was investigated for the first time in females of Thermobia domestica. Topical applications of this compound, which has been said to possess anti-juvenile hormone activity, were carried out at various times in the postecdysial period of a reproductive cycle, during intense vitellogenesis in the terminal oocytes. The effects of treatment were observed on mortality, fecundity, insemination and also on the ultrastructure of corpora allata; they depend on the dose used and on the day of treatment. A single application of 10 μg/insect at the beginning of the postecdysial period induces antigonadotropic effects in females reared both with and without males. The effects of precocene add to those of non-insemination, which also elicits inhibition of oocyte maturation. In addition, the cytotoxic action of precocene, leading to degeneration of the corpora allata, which is most probably irreversible, was demonstrated.

The development of the collagenous endoskeletal structures or endosterna and of the basement membranes of epithelial cells have been studied histologically during postembryonic development in the first 3 nymphal instars of the firebrat, Thermobia domestica. During the postembryonic instars fibroblasts produce collagenous ligamentous bridges, and a fibrillar basement membrane is formed by the epidermal cells. These fibroblasts and epidermal cells form a matrix with many orientated collagen fibrils, which have a banding periodicity of 600 A.

1. 1. Ovaries of Therobia domestica, dissected from inseminated females and incubated with tritiated amino acids, synthesize labeled proteins, the major fraction of which is indistinguishable from the major vitellogenin secreted by the fat body, when considering the electrophoretic mobility, the polypeptide composition and the immunoreactivity. 2. 2. Peptide mapping, using two different proteases, shows a striking structural similarity between the proteins of both origins and reveals interrelationships between their subunits. 3. 3. The ovary synthesizes the 210–212 kD precursors of the major vitellogenin, as does the fat body, and processes them intensively into smaller subunits (176–182, 57 and 46 kD). The follicle cells are tentatively nominated for both roles. 4. 4. The quantitative contribution of the two ovaries to the vitellogenin pool was found to be much higher than that of the fat body.

A case of spontaneous infection of Malamoeba locustae from a free-living indoor population of Lepisma saccharina is reported. The source of infection was probably a culture of Schistocerca gregaria reared in the same room. Measurements of fixed cysts from L. saccharina are compared with measurements of fixed and unfixed cysts from S. gregaria and with published data from other species of grasshoppers and locusts.

A topical application of precocene II (10 μg/♀) in adult females of the firebrat, Thermobia domestica , has anti-gonadotropic effects and also causes modifications of the intermoult length, the results varying according to the day of treatment. In non-treated females, which are normally inseminated at the beginning of each interecdysial period, this period can be divided into 2 parts separated by oviposition which takes place near the middle of the stadium (day 5). Treatment during the first part of a stadium generally induces slower growth of the vitellogenic oocytes and/or slower resorption of these oocytes, leading to a lengthening of this part of the stadium. The second part of the interecdysial period, marked by the pre-vitellogenic growth of the basal oocytes and their preparation for yolk deposition, has a constant length of 4–5 days and always remains synchronized with the moulting events. Treatment after oviposition most often has no effect on the concerned stadium, but modifies the length of the following stadium. In females treated on day 5 the daily variations in the haemolymph ecdysteroid levels are similar to those of control females, but with a-day delay in the peak, corresponding to an equal delay of ecdysis. The present results are discussed in comparison with previously reported data concerning the effects of precocene on the corpora allata and on the titres of juvenile hormone.

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.

An antiserum raised against the major fractions (240 + 300 Kd) of the vitellins extracted from maturing oocytes of Thermobia domestica, allowed the immunological relationship between these proteins and their haemolymph precursors (vitellogenins) to be established, as well as the female specificity of these protein fractions. Using rocket immunoelectrophoresis, the vitellogenin concentration in the female haemolymph was measured on each day of a reproductive cycle. The changes in vitellogenin titre appear to be correlated with ovarian maturation: very low levels during the previtellogenic phase and increasing levels during the vitellogenic growth phase of the basal oocytes. Also, these changes are synchronized with the moulting cycles which persist in the adults of these primitive insects. An insemination at the beginning of the interecdysial period causes a large increase in the vitellogenin titre synchronized with accelerated oocyte growth.

1. The free (physiological) amino acid profile in the brain tissue of Lepisma saccharina and Thermobia domestica (Thysanura, Lepismatidae) was investigated. 2. Nitrogenous waste products (ammonia and urea) together constituted 28% of the total ninhydrinpositive compounds for both species. 3. GABA accounted for 3% of the total ninhydrin-positive compounds in the brain of L. saccharina , and T. domestica. 4. Glutamate comprised 7% of the total ninhydrin-positive compounds in the brain of L. saccharina , and 8% in T. domestica. 5. The most abundant amino acids were alanine, proline, arginine and taurine. 6. The possible role of amino acids as neurotransmitters and/or modulators of neurotransmitter activity is discussed as well as the comparative free amino acid composition of the brain tissues of various arthropod groups.

The present paper gives an ultrastructural description of the glandular epithelium of the receptaculum seminis of Thermobia domestica . The functional units of this epithelium, belonging to the third type, are composed of 4 apically surrounding cells: a central ciliary cell, which is permanent (only the “cilium” degenerates at each molt), a glandular cell and 2 enveloping cells. An efferent ductule allows the secretory products to be released into the central lumen of the receptaculum, lined by a thick intima. During each moulting cycle, the glandular cell shows several phases of secretory activity. The role of the receptaculum seminis is considered, both as a storage organ for seminal liquid, and as a possible source for some kind of information required for complete maturation of oocytes.

This is the first investigation concerning prostaglandin-like compounds in the primitive insect, Thermobia domestica. The incubation of homogenates of reproductive tissues in the presence of [U-14C]arachidonic acid yielded several compounds which have been characterized by their chromatographic mobilities as well as by the enzyme systems involved in their formation. The three major compounds (I to III) had Rf values very different from those of several prostaglandin standards (PGE2, PGF2α and 6-keto PGF1α). As the addition of aspirin or indomethacin had no effect on the conversion of arachidonic acid, a cyclo-oxygenase pathway leading to prostaglandins seems to be excluded. However, another compound (noted V), present in very small quantities, could be a prostaglandin, owing to its chromatographic mobility near that of the PGE2 standard. By contrast, compounds I and II co-migrated with 8- and 5-hydroxyeicosatetraenoic acid standards, respectively, and the addition of 4,7,10,13-eicosatetraynoic acid (ETYA) or nordihydroguaiaretic acid (NDGA) showed a pronounced and dose-dependent inhibition of arachidonic acid conversion. These data demonstrate lipoxygenase activity. Such a pathway in the metabolism of arachidonic acid had not, as yet, been reported in insects. This enzyme system can be demonstrated in the genital tract of the male and also in the seminal receptacle of the female, especially after insemination. So the enzyme system is probably transferred from male to female during mating.

We have conducted a reinvestigation into both the identification and quantification of juvenile hormone (JH) from several developmental stages of the cockroach, Nauphoeta cinerea , and the firebrat, Thermobia domestica , using a gas chromatography-mass spectrometric (GC/MS) method. We detected only JH III in these animals in contrast to prior studies in which JH I, II, and/or III had been reported using a different scheme relying on HPLC purification and subsequent GC/MS analysis under chemical ionization (CI) conditions. Very high levels (∼800 ng/g) of JH III were found in N. cinerea embryos at stages after dorsal closure whereas first stadium nymphs and female penultimate stadium nymphs contained only low levels (∼1 ng/g and ∼7 ng/ml respectively); in adult females at the stage of rapid oocyte growth ∼150 ng JH III per ml of hemolymph was measured. T. domestica nymphs and egg laying adults contained only low levels (∼1 ng/g) of JH III. The results emphasize the caution which must be used in interpreting results of procedures for analysis of JH at parts-per-billion levels, and also enforce prior observations that the higher JH homologs are not present except in the Lepidoptera .

Strong spatial and temporal niche separation exists among seven dune dwelling Lepismatidae. Lepismatids are divided spatially into two groups occupying the slipface and vegetation clump habitats respectively. Variation in spatial use may be explained as a response to the physical environment and may be related to species’ morphological adaptations to physical parameters within dune habitats. Temporal use is divided into diurnal and crepuscular, nocturnal, and dawn active groups. Variation in temporal activity patterns may be explained as a response to specific weather conditions and may be related to species’ physiological adaptations that allow activity under specific weather regimes.

1. 1. A highly efficient cellulose digestion could be demonstrated in a primitive insect species, Thermobia domestica (Thysanura:Lepismatidae), by the application of a uniformly 14 C-labelled substrate. 2. 2. Gut extracts exhibit distinct hydrolytic activities toward different cellulosic substrates (cellobiose, sodium carboxymethylcellulose and microcrystalline cellulose). Therefore, the complete cellular complex must be present. 3. 3. Besides cellulases, several other carbohydrates occur in the digestive juice, thus reflecting the omnivorous feeding habits of the insect. 4. 4. The crop was found to be the main site of carbohydrate digestiopn, also including cellulolysis. 5. 5. It is very likely that the cellulolytic enzymes derive from the gut tissues of the firebrat.

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.

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.