INTERNAL SECRETION OF TESTICLE 197 



Lately Benoit (1922 a), a pupil of Bouin, has made observations 

 on different species of birds, and concluded that there is a close 

 correlation between the nuptial plumage and the interstitial 

 cells, whereas no such correlation exists between the sex 

 character and the generative part of the testicle. Different 

 objections have been made by Pezard (1923 a). 



Investigations on the cyclic changes of the interstitial 

 tissue in birds have been made by Watson (1919). The histo- 

 logical observations of Watson on the greenfinch are of interest 

 in this connection. As in the mole, the greenfinch shows a rela- 

 tive decrease in the number of interstitial cells during oestrus. 

 But it seems that marked cyclical changes of a cytological nature 

 take place also in the interstitial tissue. This question must be 

 investigated in greater detail and by special cytological methods ; 

 but what Watson stated, indicates that the fibrous tissue cells 

 gradually disappear in the interstitial tissue, and are replaced 

 by another type of cell. These seem to be the true interstitial 

 cells massed together in the angles formed by the greatly 

 increased tubules. Similar statements were made by Benoit 

 (1923 a). 



Certainly more detailed histological investigations are neces- 

 sary. First, it is essential to define in a stricter sense what kind 

 of cells precisely are understood under the name "interstitial 

 cells," and in every case. Differential histological methods 

 should be applied more closely. Secondly, further criticism is 

 necessary in regard to all questions concerning the quantity of 

 the interstitial cells. 



On the other hand it is unjustifiable and arbitrary to declare 

 that some tissue cannot be considered as having an endocrine 

 function because it is "connective tissue." The notion of 

 connective tissue. is very indefinite, and where such tissue is 

 present it may undergo cyclic changes like the interstitial 

 cells in mammals. It suffices to glance at Fig. 57 where a tissue 

 which seems to be simply connective step by step becomes 

 transformed into an agglomeration of interstitial cells. There 

 is no fundamental reason why cells which are connective 

 tissue cells by origin should not form an organ of internal 

 secretion, and if further embryological investigation should 

 show that, contrary to Rubaschkin's view, the interstitial cells 

 are really mesenchjnne cells, as supposed by Bouin and Ancel, 

 this need not modify our conclusions as to the endocrine 



