MALE REPRODUCTIVE CELLS 



441 



gated nucleus and its posterior end is much curled. The cell body 



extends, as a middle piece, back from the distal end of the head for 



about the same length that 



the head is. It invests the 



axial filament of the tail, and 



distally the tail emerges and, 



except for the fin which is 



not shown, is free for the rest 



of its course. The nurse-cell 



nuclei at this time have moved 



up from the flat position which 



they occupied before and lie 



alongside of the heads of the 



spermatids which are attached 



to them. They are rounder 



and fuller than before. 



The last stage to describe 

 is shown in Figure 405. This 

 shows how the spermatids 

 have shortened 

 straightened the 



been gathered mtO Close FIG. 403. Spermatids of Raja ocellata. The nuclei 



are lengthening and the tails are forming. Above 



in length, 

 head, and 

 into close 

 points 



are a number of tails cut transversely and showing 

 the outlines of the cells whose centers they occupy. 

 These reproductive cells form two sperm columns, 

 which are placed opposite to two large nurse cells 

 on the basement membrane. X 1000. 



bundles. Their points are 

 still buried in the nurse cells, 

 and the nuclei of these later 

 cells are now large, full, and 

 have well-developed chro- 



matin structure, as well as a larger nucleolus than before. A rather 

 remarkable vacuole appears at this time in the cytoplasm of the nurse 

 cell and is filled with a dense mass that stains gray in iron haema- 

 toxylin. This mass rests against the distal end of the nurse-cell nucleus 

 and is probably connected in some unknown way with the nutritive 

 processes which are going on at this time. Other smaller granules appear 

 in the proximal cytoplasm. It should be noticed in both this stage and 

 in the last that the head of the spermatid is connected with the basement 

 by a transparent strand of cytoplasm which passes through the body of 

 the nurse cell. The spermatozoa are now nearly ripe, and it is in this 

 condition that they separate from the nurse cell and pass out of the lobe 

 with the rupture of the lobule at its surface. The nurse cells remain 

 behind, showing more individuality at this time than at any other period 

 of their lives. Three of them are shown by Figure 406 rising from the 

 inner wall of a recently ruptured follicle. 



The above description of the production of spermatozoa furnishes 



