STUDIES ON GERM CELLS 425 



ularly the chromatin, contains the determiners of hereditary 

 characteristics. Furthermore, nuclear division without the forma- 

 tion of chromosomes obviously condemns the hypothesis of the 

 genetic continuity of the chromosomes, and hence seriously inter- 

 feres with current ideas regarding the significance of the accessory 

 chromosomes in the deterimnation of sex. Among the animals in 

 whose germ cells amitosis has been reported are certain amphibia, 

 coelenterates, cestodes, and insects. 



Amphibia. Vom Rath ('91, '93), Meves ('91, '95) and Mc- 

 Gregor ('99) have recorded amitosis in the germ cells of Amphibia. 

 Meves claims that the spermatogonia of Salamandra divide 

 amitotically in the autumn but return to the mitotic method in 

 the spring, later giving rise to functional spermatogonia. Vom 

 Rath finds amitosis but contends that the cells which divide in 

 this way do not become spermatozoa but are degenerating, 

 being used as nutritive material by the other spermatogonia. 

 The amitotic divisions described by McGregor ('99) in Amphiuma 

 differ in certain respects from those of both Meves and vom 

 Rath. In this species the primary spermatogonia divide by 

 amitosis, their products later divide by mitosis and produce 

 functional spermatozoa. Our knowledge concerning amitosis 

 in the spermatogonia of ^^nphibia is therefore in an unsatis- 

 factory state, although the observations of Meves and McGregor 

 argue strongly in favor of this method. 



Coelenterata. While no direct nuclear divisions were recorded 

 by Hargitt ('06) in the germ cells of Clava leptostyla the absence 

 of mitotic figures in the early cleavage stages of the egg led him 

 to the conclusion that the 'nuclear activity differs greatly from 

 the ordinary forms of mitosis, and appears to involve direct or 

 amitotic division" (p. 229). If this were true the germ cells 

 which are derived from these cleavage cells must be descended 

 from cells which once divided amitotically. This case of sup- 

 posed amitosis has been cleared up by the subsequent studies 

 of Beckwith ('09) who collected material' of Clava very early in 

 the morning and found typical mitotic divisions during the 

 maturation and early cleavage of the egg and no evidence of 

 amitosis. 



