THE REPRODUCTIVE ORGANS 



409 



considerable empty spaces or may be loosely filled with cells. In some cases large 

 quantities of cells may be present, but the densely packed tubules which are found in 

 the testis in May for example are practically never seen. In April and May sperma- 

 tozoa are also present in much increased quantities, and the appearance of the sections 



■ — h 



Fig. 142. Germ cells in normal testis. 



a., spermatogonia; 6., spermatocytes; 



c, spermatids. 



d 



Fig. 143. Germ cells in normal testis. 



a., spermatogonia; h., spermatocytes; 



f., spermatids; d., spermatozoa. 



Fig. 144. Section of active testis of Fin whale during the male sexual season. 



indicates unmistakably an active proliferation of germ cells, and a speeding-up in the 

 production of spermatozoa. In Figs. 144 and 141 this active condition of the testis 

 can be compared with the relatively passive condition. It happens rather often in a 

 testis in the latter condition that the section of a tubule shows numerous spermatozoa 

 which may be as abundant as in the active testis, but the distinction lies in the fact that 



