440 



HISTOLOGY 



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FIG. 401. Second reduction divisions by the sec- 

 ondary spermatocytes of Raja oscellata. X 1000. 



Figure 402 shows two sperm 

 columns, each extending dis- 

 tally from the nurse cell which 

 belongs to it. It can here be 

 noticed that each column is 

 cup-shaped, and that its sec- 

 tion forms an elongated loop 

 with the bend placed against 

 the nurse cell. The nucleus 

 has moved to the proximal 

 end of the cell in each sper- 

 matid, and a filament, the devel- 

 oping tail, passes distally from 

 the nucleus out of the end of 

 the cell. 



Figure 403 shows a consid- 

 erable advance on the last 



stage. The cells have all moved proximally, in the three sperm 

 columns shown, and have gathered closely in the loop by the basal 

 nurse cells. These latter have remained flat. Each spermatid has 

 become much elongated and so has the nucleus, which is pointed 

 distally and has a ring-like -.- 



enlargement at its flat distal 

 end. The cell outlines are 

 poorly shown, but where cut 

 transversely as shown in the 

 upper part of the figure 

 their outline is quite ap- 

 parent with a dot, repre- 

 senting the tail, in the 

 center of each. 



The change from this last 

 stage to that seen in Figure 

 404 is somewhat wide, but 

 space forbids a closer com- 

 parison. In the latter stage 

 the half-developed sperma- 

 tozoa have greatly length- 

 ened and have all moved 

 down so that their sharp 



heads are buried in the FIG. 402. Two nurse cells and two sperm columns 



composed of young spermatids in Raja ocellata. The 

 tails and end-knobs are beginning to form. Cell 

 walls are still complete. X 1000. 



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