| Summary: | The process of normal spermatogenesis was investigated in six species of the genus Dermestes (D. haemorrhoidalis, D. ater, D, peruvianus, D. lardarius, p. frischii, D. maculatus and D. vulpinus). In all of the species germ cells are connected with each other by cytoplasmic bridges and surrounded by an envelope consisting of one or more cyst cells. Therefore the time of isolation of the new predefinitive spermatogonia (A0) can be determined directly by counting the number of cells in individual cysts. Once differentiation begins, the spermatogonia undergo a series of more or less synchronous mitoses during which they change progressiveiy in important characteristics: their size diminishes and their number per cyst (i.e. 2n) increases. These changes are in the direction of, and preparatory to, meiosis. The number of generations of secondary spermatogonia is 7 in D. haemorrhoidalis, D. ater, D. peruvianus and D. lardarius, 6 in D. frischii, D. vulpinus and D. maculatus. In D. maculatus the duration of the mitotic cycle almost always shows no change in the duration of S- or G2- through 6 generations of spermatogonia with a steady cell cycle time of 20 hrs. The primary spermatocyte, while its nucleus undergoes the conspicuous changess of meiosis, characteristically grows to about 11 fold its starting volume in D. haemorrhoidalis, 8 fold in D. star, 5 fold in D. peruvianus, 9 fold in D. lardarius, 11 fold in D. frischii, 7 fold in D. vulpinus and 6 fold in D. maculatus. No typical leptotene, zygotene, pachytene or diplotene stages are visible because the euchromatic regions remain diffuse until diakinesis and diakinesis is of short duration in Dermestes. The duration of the meiotic cycle in Dermestes is correlated weakly with DNA content and varies from 12.75 days to 19 days for the period pre-meiotic S-phase to elongate spermatid. In Dermestes a certain number of germ cells die. The great majority of cell deaths occur at definitive periods of development of the spermatocytes. As far as the responses of spermatogonial and spermatocyte cells of Dermestes to x-irradiation are concerned it has been shown that: a) The last two generations of spermatogonia (In-type & B-type) appear to be the most sensitive to cell death; b) Damaged spermatogonia of all types degenerate either in interphase or upon entrance into prophase of their first post-irradiation division. The commonly-observed lack of metaphase is obviously accounted for by the degeneration in earlier stages; c) Repopulation of any follicle depends on the number of type AO spermatogonia present along the germarium membrane after irradiation; d) Spermatocytes are more sensitive to the induction of cell death at early prophase-I rather than late prophase-I; e) The distinct phenomenon of "stickiness" of the chromosomes appear to be due to a generalised physiological process; f) On the basis of dose-response kinetics, there is a variation between species with D. haemorrhoidalia being the most resistant and D. peruvianus and D. lardarius the most sensitive to x-irradiation induced spermatocyte cells death; g). On the basis of dose-response curves, A0 spermatogoniam appeared to be more resistant to x-rays induced cell death in D. haemorrhoidalis and more sensitive to x-rays induced cell death in D. lardarius; h) Distribution of cell-number in spermatocyte cysts which surviv ex-irradiation shows that a fixed proportion of cells may be lost but then the whole cyst dies. Cells may still die in small groups before this catastrophe occurs; i) There is a significant correlation between high exposure (i.e. exposure, giving 10% survival) and spermatocyte nuclear volume. The model for maintenance of a continuing supply of spermatogonia during adult life suggests that there is a group of AO spermatogonia in each follicle which divide quasidichotomously with one becoming a new A0 spermatogonia (responsible for the next generation of germ cells) and the other (the definitive spermatogonium) destined, through multiplication and differentiation, to give rise to the mature spermatozoa. The model proposed here for Dermestes species (Coleoptera) is in good agreement with other models, suggested for different orders of Insecta. The numbers of A0 spermatogonia in each follicle are estimated for each Dermestes species studied. The likelihood of sterilization of a male Dermestes depends upon three factors: i) The number of follicles per testis; ii) The number of AD cells per follicle; iii) The inherent sensititity of the AD cells.
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