234 R. R. HUMPHREY 



cells with rounded nuclei and much cytoplasm proved fruitless; 

 neither could satisfactory evidence of amitosis be secured. 

 Finally, turning to an intermediate period, I found that in animals 

 killed September 25th and October 7th and 21st, in the caudal 

 portion of the testis, between lobules then occupied by mature 

 spermatozoa, mitoses were to be frequently found among those 

 nuclei just beginning to thicken or become rounded. Figures 

 10, 11, and 27 show such mitoses. It would appear, then, that 

 the most favorable time for mitosis is before the cell has become 

 burdened with lipoid accumulations and increased cytoplasmic 

 content. More rarely divisions are found in later periods; one 

 each was observed in animals killed October 30th, December 

 10th, and December 12th. In each of these cases the mitotic 

 figure was found in a group of lipoid-filled cells, the accumulations 

 in the dividing cell being pushed to one side, away from the 

 spindle. In no material killed in later winter or spring months 

 have mitoses been noted. That mitoses are most to be expected 

 in the earlier growth period of the interstitial cells would appear 

 from the fact that mitotic figures are found to occur regularly 

 in corresponding regions of the testis in Salamandra atra, Cryp- 

 tobranchus, and Desmognathus, while in none of these three 

 forms were mitoses seen at earlier or later periods, i.e., in regions 

 of the testes where conditions in Necturus had resulted in an 

 occasional cell division. 



Mitotic division of the interstitial cells in adult mammals is 

 of infrequent occurrence. B. M. Allen ('04) found mitoses in 

 the interstitial cells of pig embryos ''up to the stage of the 7.5 

 cm. embryo, and in the rabbit testis as late as eight days after 

 birth." Both Allen and Whitehead ('04) found no mitoses in 

 older pigs; Duesberg ('18) found none in his extensive studies 

 on the opossum, though Jordan ('11) reports seeing them in this 

 animal; Rasmussen saw none in the woodchuck. Though 

 several workers — Hansemann ('95), Reinke ('96), Von Lenhossek 

 ('97), and Pick ('05) — have found mitotic figures in adult human 

 material, other workers comment upon their absence, Kasai, 

 among these, seeing but one mitotic figure in a series of 130 

 human testes — the youngest from a four months' fetus, the oldest 



