220 K. R. HUMPHREY 



The fact remains that such variations in cyclic changes do 

 exist, as well as other differences, more or less difficult of expla- 

 nation. A survey of the situation leaves one with these 

 questions : 



1. Are the variations noted due to fundamental differences 

 in the cells themselves in different animals, or are they due to 

 the varying 'balance' of many conditions, each one of which is 

 more or less obscured in complex testes? 



2. Do the testes of any lower vertebrate forms not yet in- 

 vestigated possess a structure in which the processes are more 

 separated, so that the correlations of the interstitial cells may be 

 more easily interpreted, and, if so, to what is their maximal con- 

 dition in such forms related? 



It is with the questions last stated that this investigation is 

 chiefly concerned, for a satisfactory answer thereto may be ex- 

 pected to throw some light upon the difficulties encountered in 

 testes of the more complex type. 



PRESENT INVESTIGATION 



Kingsbury ('14), at the conclusion of a paper on the inter- 

 stitial cells of the mammalian ovary, discussed briefly the corre- 

 sponding cells of the testis. He called attention to the greater 

 difficulty involved in the male than in the female organ in analyz- 

 ing the conditions underlying their appearance; he further in- 

 sisted upon the need for work on testes of lower forms in which 

 the progressive and regressive changes are more widely separated 

 in time and place, as they are in the ovary of the female. The 

 urodele amphibian possesses such a testis. In it, as will be 

 made apparent subsequently, the growth processes and degenera- 

 tive changes are isolated to an extent not found in any higher 

 vertebrate, no matter how widely separated its rutting periods 

 may be. 



To Dr. Kingsbury the writer is indebted for suggesting this 

 problem and for the generous contribution of the urodele material 

 he had collected. His helpful suggestions and criticisms during 



