SPERMATOGENESIS OF THE DRAGON-FLY. 28 1 



becomes constricted and the cells are divided. As in Fig. 51 a 

 few spindle fibers may connect the two cells. 



This is probably the true reduction division for the bivalents. 

 For the sex-chromosomes which splits equally into two parts, 

 this is an equational division. 



(d) The Second Spermatocyte Division. 



In the telophase of the primary division, the univalent auto- 

 somes are closely crowded together, but they soon separate and 

 become scattered around the edge of the nucleus in preparation 

 for the second division which closely follows the first. By actual 

 measurement these cells are one half the size of the cells in the 

 prophase of the preceding division. The univalent autosomes 

 are small and compact. The second division occurs without 

 any intermediate stages, the same autosomes which were in 

 the preceding telophase become the metaphase autosomes. In 

 polar view, they are round with no evidence of constriction and 

 are arranged in the following order: a ring of 9, enclosing three, 

 of which one is very small. This is nearly the same order as 

 that occurring in the metaphase of the first division. The sex- 

 chromosome, however, always lies outside the ring and is sur- 

 rounded by its usual vesicle. This order prevailed in all cases 

 counted although the size of the ring varied; the autosomes 

 were spread apart more in some cells and in others they were 

 collected into a smaller ring. In fact polar views of this stage 

 (Figs. 54 and 55) appear much like the telophase of the first 

 division. In Figs. 56 and 57 the sex-chromosome is not visible. 



In side views of this stage, all the autosomes are dumbbell- 

 shaped, with the two halves longer than broad. The sex- 

 chromosome is at one side of the spindle and can be identified 

 by its roundness, its vesicle and the lack of spindle fibers. Dur- 

 ing division, the sex- chromosome precedes the dividing auto- 

 somes and, undivided, goes to one pole. It may reach the pole 

 before the autosomes start their division or it may be only a 

 little in advance. In no spindle observed did it ever lag behind 

 the others. Figs. 58, 59, 60, 61, 62 and 63 show spindles of the 

 second division, with the sex-chromosome in various positions. 

 In late telophases some of the spindle fibers may clump together 



