424 



E. V. COWDKY 



old age these cells, like those of many other endocrine organs, retain 

 embryonic potencies, as is shown by their ability to undergo dedifferen- 

 tiation and give rise to tumors, as described in dogs by Goodpasture. 

 It seems that the interstitial cells of the ovary are less liable to tumor 

 formation. 



.Fig. 1. Groups of interstitial cells (i) in human testis closely associated with a 

 blood vessel (b.v. ) (magnification 680). 



The comparative growth energy of the interstitial cells has not been 

 measured by the inanition method. It would seem, however, that their 

 growth is more vigorous than that of the seminiferous tissue, since they 

 develop and function in cryptorchids. * 



Comparative Anatomy 



Interstitial cells occur in most of the vertebrates which have been 

 examined, with the possible exception of certain birds; but their degree 

 of development is subject to enormous variation in different classes. In 

 hibernating animals, like the woodchuck, they exhibit great cyclical 

 changes in number (Rasmussen (a)). During the hibernating period they 



