PROCESS OF REPRODUCTION IN ORGANISMS. II 



But Boveri's recent work on polyspermic and centrifuged eggs 

 of Ascaris (Boveri, '10) throws new light on this case. Accord- 

 ing to Boveri it is the cytoplasm of the egg that determines 

 which nucleus or nuclei shall undergo diminution and which shall 

 not. All nuclei which come to lie in the animal half of the egg 

 undergo diminution, while those which lie in the vegetative half 

 remain undiminished. If, as most supporters of the germ plasm 

 hypothesis believe, the nuclear substance is the real germ plasm 

 then how shall W T C account for the fact that here in Ascaris it is 

 the cytoplasm that determines which nuclei shall persist as germ 

 plasm and which shall become somatic. The cytoplasm is not 

 properly speaking a part of the germ plasm at all, if we accept 

 the hypothesis in its original form, but rather represents in the 

 egg a differentiated soma, yet if Boveri's conclusion is correct 

 the cytoplasm determines the localization of the germ plasm. 

 Apparently then in this classical case of Ascaris, which has been 

 so often quoted as an irrefutable support of the germ plasm 

 hypothesis, the visible distinction between germ cells and soma 

 is determined by cytoplasmic differences along the egg axis. If 

 this is actually the case, the germ plasm is certainly not an 

 independent entity here, but is determined in the same way as 

 many other early embryonic differentia cions, i. e., by its environ- 

 ment within the organism. 



In Cyclops and various other forms the "Keimbahn" is char- 

 acterized only by certain cytoplasmic granules which do not 

 appear in other cells and by less rapid division. The fact that, 

 at least in some cases these granules originate from nuclei of other 

 cells which have been taken up by the egg, as certain authors 

 have shown, does not alter the case. If the granules are de- 

 termining factors then the germ plasm is determined by factors 

 in the organism external to it. If they are not determining fac- 

 tors the existence of a-"keimbahn" indicates merely that the 

 germ plasm normally arises from a certain part of the organ- 

 ism. These cases then,, like that of Ascaris, afford no real 

 evidence of the continuous existence of undifferentiated germ 

 plasm. 



Investigations of recent years have shown that in at least many 

 cases among the lower vertebrates the primitive germ cells 



