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 



^Vn*tfK$5%\ "Vifc 



FIG. 399. Tetrad formation and first reduction 

 divisions in Raja ocettata. X 1000. 



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

 _.. ..-v -......- .. ^.-v.^ 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 

 another. No changes have 

 occurred in the position or 

 appearance of the nurse cells. 

 The lower part of figure 401 



FIG. 400. Second spermatocytes of Raja ocellaia. ^ f t u _ divisions 



Nurse cells on basement membrane. The repro- f n< U1V1MUI1S, 



ductive cells begin to show a tendency toward the in the latter Stage S. To the 

 formation of sperm columns. X 1000. 



right are ^^ ^ TeS u\tS of 



these divisions, the youngest spermatids. The development of these 

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



