182 The Spermatogenesis of Abraxas 



the first division are mostly arranged round the membrane, and 

 approach 50 in number (Fig. 13). As the division approaches there 

 are indications that these small chromatin masses become associated 

 in pairs, and before the spindle is formed between 20 and 30 of these 

 pairs may be counted (Fig. 14). This doubleness is much less pro- 

 nounced in spermatocytes of the first type, and in them the preliminary 

 diploid condition is not found. The first division of these smaller cells 

 differs greatly from that described above, for the equatorial plate is so 

 irregular that an exact count has never been possible ; the number of 

 chromosomes, however, approaches 28 (Figs. 15, 16). The anaphase 

 figures are very remarkable ; at the beginning the chromosomes usually 

 show a dumbbell-like shape, but they do not all divide simultaneously, 

 with the result that while those in the centre of the equatorial plate 

 still retain their position, those near the edge have divided and the 

 halves may have nearly reached their respective poles. The spindle 

 thus may appear almost covered with scattered chromosomes, which 

 finally all reach the poles ; a vesicular nucleus is then formed and the 

 cell divides (Fig. 17). 



The second spermatocytes appear to begin their division almost 

 immediately; it is essentially like the first except that the cells, 

 spindles and chromosomes are distinctly smaller and the arrangement 

 of the latter even more irregular (Figs. 18, 19). At the close of the 

 division the cells become spermatids, with a vesicular nucleus and 

 conspicuous "Mitochondrion Korper," differing from those produced 

 by the large regular spermatocytes only in their smaller size (Fig. 20, a, h). 



It will be seen that the process described is closely similar to that 

 found by Moves in Pygaera, except that a single spermatid nucleus 

 is formed instead of each chromosome forming a small separate vesicle. 

 Abraxas also differs from his description in the fact that the " normal " 

 spermatogenesis occurs chiefly in the late larval and early pupal stages, 

 and the small irregular spermatocytes are most conspicuous in the 

 rather later pupae. In my first sections of pupae several days old 

 I found no large regular spermatocyte divisions, and even in pupae 

 3 — 5 days old they are often quite scarce; while in larvae not yet 

 spun up some search may be required before the small irregular type 

 is founds According to Moves both types occur in about equal 

 numbers in the pupae of Pygaera. 



^ I owe the suggestion that the regular type might occur more frequently in larvae, and 

 that the irregular type may be abnormal, to Prof. E. B. Wilson, who has kindly examined 

 some of my preparations. 



