164 EZRA ALLEN 



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In this connection Winiwarter ('12) (man) states: ". . . . 

 les noyaux poussiereux et croutelleux de la spermatogonese 

 me semblent representer des generations successives d'une seule 



et meme categorie d'elements : les spermatogonies " 



He does not find them as clearly differentiated as Regaud does in 

 the rat. 



As to the number of divisions of the spermatogonia before the 

 final one, much has also been written. I am inclined to think 

 with Schoenfeld that some spermatogonia! daughter cells must 

 form spermatogonia as long as spermatogenic activity persists, 

 while others end their career in the differentiation of spermato- 

 cytes very early — in fact, some with the production of the earliest 

 spermatocytes. Conditions in the young tubule indicate clearly 

 that at no time are all the cells of type A exhausted, though their 

 relative number decreases enormously from time to time (com- 

 pare figures 3 and 6). Btit they increase again actually and 

 relatively during the growth stages of the spermatocytes, as is 

 seen by comparing figure 6 with figure 8, the latter showing many 

 more of type A than the former. 



It would appear from these figures, especially figure 5, as well 

 as from conditions found in the adult tubule, that each daughter 

 cell of those spermatogonia which give rise to spermatocytes 

 becomes a spermatocyte — not one a new spermatogonium and 

 one a spermatocyte. This conclusion necessitates that certain 

 spermatogonia (or indifferent cells) are always present in a tubule. 

 These must continue their line by cell division, as brought out 

 in the preceding paragraph. When this supply fails the function 

 of the testis must cease. At what age this cessation occurs has 

 not been determined. ^ The problem thus becomes one of differ- 

 entiation associated with the wave-like manifestation of energy 

 which finds expression in the complex activities of the sperma- 

 togenic tissue — cell division, maturation, growth changes of the 

 spermatids, and the activities of the Sertoli cells correlated with 

 the ripening of the spermatozoa. 



1 While this manuscript was in press, I studied testes from old rats of the Wistar 

 colony, some nearly two years of age — the oldest obtainable. In these spermato- 

 genesis is normal. Rats two years old are likely to die at any time. 



