MALE REPRODUCTIVE CELLS 



437 



FIG. 394. Two very young 

 spermatic lobules in the tes- 

 tis of Raja ocellata. The 

 larger one shows a begin- 

 ning of the lumen (/.) and a 

 differentiation of nurse cells 

 and spennatogonia. X 1000. 



These latter become the 



these lobes the sperm is constantly maturing during the breeding 

 season and is then thrown off and collected for use through the vas 

 deferens. When once a good section through a 

 germinal center is found, it is comparatively 

 easy to follow all the stages of sperm develop- 

 ment by their comparative distances from this 

 point as well as their actual structure. 



The single primitive reproductive cells seen 

 in Figure 393 are probably a peculiar stage in 

 themselves. We may call them the pre-sper- 

 matogonia. Each one is the originator of a 

 single lobule, and all the reproductive and 

 nurse cells in it. Its covering of several con- 

 nective-tissue cells is a separate structure, and 

 forms all subsequent capsule tissues. During 

 the first divisions as pictured in Figure 394 it 

 can be seen that the divisions of the reproduc- 

 tive cell have resulted in what can already be 

 distinguished as larger, round, nucleated sper- 

 matogonia, and smaller cells with oval nuclei, 

 nurse cells. 



In the skate and all elasmobranch fishes we have a case of early for- 

 mation of the lumen in each lobule. This was already indicated in the 

 larger lobule of Figure 394, and it is now very complete in the single 

 lobule, one half of which is represented in Figure 395. The two kinds 

 of cells are very irregularly arranged in the resulting germinal epithe- 

 lium, but when growth has progressed to the stage seen in Figure 396, 

 which represents a small portion of a section of one of the lobules, it can 



be seen that the reproduc- 

 tive cells all have a proxi- 

 mal position and the nurse 

 cells have a distal position, 

 forming a single row on 

 the edge. A rather re- 

 markable change begins to 

 take place now, as is indi- 

 cated in this figure by the 

 withdrawal of two of the 

 nurse cells proximally. 

 This change consists in a 

 migration of all of the 

 nurse cells to form a single proximal layer on the capsule wall, leaving 

 the many layered reproductive epithelium on the distal surface. 



FIG. 395. Section of one half of an older lobule than 

 seen in Fig. 394. n.c., nurse cells ',ogn., spermatogonia. 

 X 1000. 



