192 INTERNAL SECRETIONS 



themselves into polyhedric interstitial cells disposed around the 

 blood vessels. At this time the development of such sexual char- 

 acters as the head apparel also begins. Des Cilleuls concluded 

 from his observations that there is in the cock a parallelism in 

 the development of the interstitial tissue and that of the sexual 

 characters. 



The detailed investigations made by Boring and Pearl (1917) 

 are opposed to these observations of des Cilleuls. Boring and 

 Pearl examined more than 60 birds from chickens just hatched 

 to eighteen-months-old cocks. In the former they found a 

 small number of interstitial cells, whereas in older birds 

 interstitial cells were never detected. According to Boring 

 and Pearl the interstitial cells in the testicle of the cock dis- 

 appear at the age of about six months. They think that the 

 observers who found interstitial cells in the testicle of the cock 

 (des Cilleuls, Mazzetti and Reeves) were misled by small 

 pieces of tubules surrounded by connective tissue. Boring and 

 Pearl observed in their preparations several places which 

 resemble the illustrations of groups of interstitial cells. They 

 point out "that the only way to be sure of interstitial cells is 

 to use a differential stain." Boring and Pearl claim to have 

 used such a stain, since they employed osmic acid for blackening 

 the fat and several differential stains for secretion granules of a 

 protein nature, and they say that there is "no possibility of 

 missing secreting cells when these stains are used, if there are 

 any present." Boring and Pearl conclude from their obser- 

 vations that true interstitial cells are not a necessary or a 

 constant element in the testicle of the cock. Basing their 

 position on these histological and other observations made by 

 them on the gonads of hermaphrodite birds (1918) they con- 

 cluded that the interstitial cells have probably no influence 

 on the development of the sexual characters in the fowl. 



The question was examined dlsohyPezard^i^iS, pp. 109-117) 

 who confirmed the statement of des Cilleuls, Reeves, Boring 

 and Pearl as to the presence of interstitial cells in the testicle of 

 the young chicken. But like Boring and Pearl, Pezard states 

 that at the end of the second and at the beginning of the third 

 month the interstitial tissue decreases; as he points out, this 

 decrease is possibly only an apparent one, as by this time 

 the generative part is more markedly increased than the 

 interstitial tissue. The interstitial tissue continues to decrease, 



