D. W. CUTLKH AND L. J)(UNCA.STEK 67 



numerous and form the greater part of the whole organ ; tlie cells in 

 them may be arranged in layers according to the condition of the 

 various cells in the development of the sperm. The lowest layer, that 

 nearest the wall of the tubule, is composed of spermatogonia among 

 which lie the Sertoli cells; these are characterised by their lightly 

 stained cytoplasm, their irregularly shaped nuclei, and the presence of 

 a distinct nucleolus; in the human testicle a rod has been described as 

 present in each of these Sertoli cells, but in the cat we have been 

 unable to detect it with any degree of certainty. 



The next layer of cells are spermatocytes for the most part and 

 in them can be seen the mitotic figures in various stages of division ; 

 while the centre of the tubule is almost entirely filled with mature 

 sperms. 



Testes of Tortoiseshell Cat. 



As already mentioned the most conspicuous differences between the 

 testes of the normal and tortoiseshell torn cat are the abundance in the 

 latter of interstitial tissue and the entire absence of the spermatogenesis 

 within the tubules (Fig. 2). Turning now to detail, of which a high 

 power drawing is given in Fig. 3, we see that the interstitial tissue 

 is similar in nature to that of the normal cat, the two types of nuclei, 

 d.n., c.n. already mentioned, can be easily detected, though the dark 

 type is less abundant than the light ; there are also the same darkly 

 stained bodies scattered throughout the cytoplasm which were to be 

 found in the normal male cat (d.g.). The cells are more vacuolated 

 than in the normal testis, but otherwise the interstitial tissue hardly 

 differs from that of the normal testis except for its much greater 

 amount. 



The tubules are smaller than those of the normal cat, and there 

 is always a distinct lumen in the centre. The cells round the periphery 

 resemble Sertoli cells but there is no trace of normal spermatogonia nor 

 of mitotic figures. The Sertoli cells are found in a small amount of 

 protoplasm which is possibly the remains of the degenerated spermato- 

 gonia ; this pnjtoplasm is vacuolated and strands pass from it into the 

 centre of the tubules. 



A section of the epididymis also demo!istrates that although this 



part of the generative system is normal in structure, yet the centre of 



the tubes are entirely devoid of spermatozoa, while in the normal case 



the lumen is practically full of them. 



5—2 



