291 



wall and characterized by sharp contour and intense staining capacity 

 (Figs. 31 — 33). Immediately the secondary spermatocyte enters upon 

 the prophase of the second maturation division. The nuclear reticulum 

 passes through the fine, coarse and segmented spireme stages. Ob- 

 viously, since the accessory chromosome passed undivided to one pole 

 during the previous maturation division only one of the resulting 

 daughter cells can contain this body. A pair of such daughter cells 

 is shown in Figure 34. Obviously again, these cells must show a 

 disparity in their chromosome groups at metaphase, one half of 

 the cells containing one more (the accessory) chromosome than the 

 other half. 



This failure of division on the part of the accessory chromosome 

 in the first maturation mitosis results in a dimorphism of spermatozoa, 

 this consisting in the presence in one half of the male reproductive 

 cells of the accessory chromosome and its absence in the other half. 



Fig. 34. Later prophase of second maturation division. Tlie cells represent a 

 pair of daughter cells of a primary spermatocyte, one with the other locking the ac- 

 cessory chromosome. 



Fig. 35. Metaphase groups of four contiguous secondary spermatocytes, two with 

 18 chromosomes including a large U-shaped accessory chromosome and two with 17 or- 

 dinary chromosomes. 



In Figure 35 are shown the equatorial plates of four contiguous se- 

 condary spermatocytes at metaphase. They are undoubtedly pairs of 

 daughter cells of a pair of primary spermatocyte mother cells. The 

 first and third yield a chromosome count of 17; the second and fourth 

 of 18; the latter two are seen to possess a large U-shaped body at 

 the periphery of the group. A chromosome of such form is absent in 

 the other two plates; it is the accessory chromosome which was con- 

 tributed to only one half of the cells. 



The various later stages of the second maturation process are seen 

 in Figures 36 to 42. At metaphase (Figs. 36 and 39) a pair of larger 

 chromosomes is seen to lag somewhat in its entrance into the spindle. 



19* 



