L. DONC ASTER 181 



cells become very definitely arranged in follicles, in which a space 

 begins to appear in the centre. From this stage onwards threads 

 may be seen running out from the cells into the cavity of the follicle, 

 ending in small vesicles or transparent masses of cytoplasm. Frequently 

 it can be made out that these threads are attached to the centrosome 

 of the cell, as described by Meves (Anat. Am. xiv. p. 1), and in some 

 cases it appears that there are accessory threads like those figured by 

 Meves in the Bee {Arch. Mikr. Anat. Bd. Lxx. p. 414). 



From this stage onwards the fate of the different follicles varies, for 

 as Meves ^ has described in Pygaera and Voinov' in other Lepidoptera, 

 there are two distinct types of spermatogenesis. The first and more 

 normal type is found chiefly in larvae before pupation and in very 

 young pupae (1 — 3 days), but both types are found concurrently except 

 in advanced pupae, in which only the second is usually found. In the 

 first type the primary spermatocytes enlarge considerably, and before 

 the maturation divisions the nucleus contains about 28 chromosomes 

 scattered round the nuclear membrane (Fig. 2). These then form 

 a flat equatorial plate, in which 28 chromosomes may easily be counted'; 

 they are not all equal in size, but none can be identified as differing 

 conspicuously from its fellows (Figs. 3 — 5). Seen in side view, the 

 chromosomes are elongated or dumbbell-shaped, and after division 

 they travel to the poles with great regularity and form a vesicular 

 nucleus (Figs. 7, 8, 9). From the rarity of its occurrence this stage 

 probably persists but a short time, and it breaks down to give a second 

 division spindle. Here again the chromosomes are regularly arranged, 

 and 28 may usually be counted without difficulty, about half the size 

 of those of the fii-st division (Fig. 10). The cells divide (Figs. 11, 12), 

 and give rise to spermatids which develop into spermatozoa in a manner 

 closely similar to that described by Meves in the "eupyrene" spermatozoa 

 of Pygaera. 



In the second type of spermatogenesis the growth-phase of the 

 primary spermatocytes appears to be shorter, and they prepare for 

 division when their diameter is conspicuously smaller. The nuclei 

 contain a number of chromatin granules, which in the prophase of 



1 Arch. Mikr. Anat. Bd. lvi. (1900), p. 56.5, and Bd. uu. (1903), p. 62. 



- Arch. Zool. Exp. et Gin. 1903, Notes et Revues, p. xlix. 



' In one testis of a heterozygote between the grossulariata and lactieolor varieties some 

 equatorial plates appear to contain 29 chromosomes. In some figures this appears to be 

 due to the fact that a few of the chromosomes have already divided, for some are markedly 

 smaller than the rest, but in one case 29 can be counted in which there is no direct evidence 

 for division (Fig. 6). 



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