166 EZRA ALLEN 



produces both spermatogonia and Sertoli cells. These cells, 

 according to Popoff, would in the rat be the ones which I have 

 described as type A. To quote him further: 



L'unite cellulaire resultant de cette derniere transformation n'est 

 toutefois qu'une apparence; les elements que Ton observe danse cette 

 phase quoique morphologiquement semblables, etant vraisemblable- 

 ment deja diff erencies : les uns devenant spermatogonies, les autres se 

 transformant en cellules de Sertoli. 



Swift studied the chick. His conclusion is: ''The primordial 

 germ cells give rise to the spermatogonia, and the coelomic cells 

 of the germinal epithelium produce the supporting cells of the 

 seminiferous tubule." 



The mode of division of the spermatogonial chromosomes 

 seemed to me so unmistakably by longitudinal splitting that I 

 was surprised to find in von Winiwarter ('12) the following state- 

 ment: '' J'admets que pour le rat, les chromosomes de la sperma- 

 togonie ne possedent pas une structure suffissament analyzable 

 pour trancher la question (p. 159)," referring to the mode of 

 division. Duesberg ('08) figures the longitudinal division and 

 makes no exception to that as the ordinary mode. I have seen 

 no evidence to indicate another method of division, so that my 

 figure 17 is to be taken as characteristic in this respect. It was 

 not until I read von Winiwarter's statement that I thought a 

 figure showing division of the chromosomes in the spermatogonia 

 would be needed. 



The age when the first sper7natozoa are ripe 



My conclusions on this point differ markedly from those re- 

 corded by Hewer ('14). In the white rats studied by her no 

 spermatozoa appear in the lumen until the age of nine weeks after 

 birth, whereas I found them in the Wistar rats at the age of 

 37 days — 26 days earlier.^ A similar comparative precocity 



2 Some very recent studies on hybrids of gray, dilute, and yellow rats reveal a 

 markedly later onset of differentiation, but I have not yet determined the age 

 when the first crop of spermatozoa appears in either F* or later generations. Ex- 

 tracted Albinos of some crosses show much delav. 



