MALE REPRODUCTIVE CELLS 



439 



The cells formed by this division are the secondary spermatocytes; 



they are shown in Figure 400. They are sometimes hard to distin- 

 guish from the early sperma- 



tids. It can be seen here that, 



for almost the first time, the 



germinal epithelium is being 



divided into the sperm col- 

 umns. Two of these are to be 



seen in the figure, and at the 



base of each is to be seen a 



single, larger nurse cell, some- 

 times called in the male a 



Sertoli cell. The cell bodies 



cannot be separated by any 



line of demarcation, and the 



nuclei are large and lie flat on 



the basement membrane. 



The reproductive cells soon 



divide again, first expanding 



their chromatin reticulum into 



a stage which is not figured. 



The divisions of secondary 



spermatocytes into spermatids 



are seen in Figure 401. They are far smaller than the previous division 



figures of the primary sper- 

 matocyte into two secondary 

 spermatocytes. Moore de- 

 scribes the dividing chromo- 

 somes of this second division 

 as separating globules, rather 

 than rings which break in 

 halves. The cell bodies are 

 rounded and have become 

 more separated from one 



FIG. 399. Tetrad formation and first reduction 

 divisions in Raja ocellata. X 1000. 



No changes have 

 in the position or 



another, 

 occurred 



appearance of the nurse cells. 

 The lower part of figure 401 

 shows some of these divisions 

 in the latter stages. To the 

 right are seen the results of 

 these divisions, the youngest spermatids. The development of these 

 into almost mature spermatozoa is shown in the next four figures. 



FIG. 400. Second spermatocytes of Raja ocellata. 

 Nurse cells on basement membrane. The repro- 

 ductive cells begin to show a tendency toward the 

 formation of sperm columns. X 1000. 



