THE GONADS OF THE FOWL 103 



lymphatic nodules or brought into the testis by the blood-stream, 

 and the stages in their formation could be followed in some of 

 the agglomerations of wandering cells present in the connective 

 tissue, side by side with cells which had completed their evolu- 

 tion. The cytoplasm of the small lymphocytes enlarges and at 

 the same time acquires small vacuoles, preserving its basophile 

 nature for some time (fig. 23). The nucleus also enlarges and 

 the chromatin blocks so characteristic of the small lymphocyte 

 become first ragged in outline (fig. 24), then appear diffuse, and 

 finally merge into a network (figs. 25 and 26) . As the growth of 

 the small lymphocytes takes place very slowly, transitional 

 stages are abundant in the intertubular connective. Eventu- 

 ally the wandering cells become fat laden and lose their wander- 

 ing capacity. The fate of such cells could not be determined in 

 the slides. It seems likely that the fat stored in the cytoplasm 

 may be used by the actively growing cells within the seminal 

 tubules or even transformed into a specific hormone which exerts 

 its influence on those secondary sexual characters affected by cas- 

 tration in the cock-feathered bird (Loisel, Pezard). 



The fact which I wish to emphasize here is that the so-called 

 interstitial cells are modified small lymphocytes and that wan- 

 dering cells recognized as of the same origin have been described 

 in the general connective tissue. Their relative abundance in 

 the testis may be accounted for by the intense proliferation which 

 is taking place within the seminal tubules, which implies an 

 increased metabolism in their cellular contents. Since no adipose 

 tissue is found in the testis, it is possible that cells which would 

 not store fat in other organs have acquired this function in the 

 gonad as the result of definite environmental conditions, and this 

 would explain the continuous formation of fat-laden wandering 

 cells during the period of heightened sexual activity. The ab- 

 sence of such cells in some birds shows that in the event of having 

 a well-defined endocrine function they may determine the sec- 

 ondary sexual characters in the young cock, but are not necessary 

 for the maintenance of those characters. On the strength of these 

 findings, it is safe to assume that the adult cock-feathered male 

 lacks a specific interstitial tissue. 



