WEISMANNISM AND OTHER THEORIES 



405 



cam's (Walton 1918) the germ cells are similarly set aside at the seventh 

 cleavage mitosis. 



In criticizing this supposed evidence for the independence and con- 

 tinuity of the germ-plasm Child (1915) points out that, since undi- 

 minished cells may give rise to other cells as well as germ cells in the early 

 divisions, the process observed may represent merely a segregation of 

 different organs rather than a separation of the germ-plasm from the 

 soma; and that the non-diminution of the chromatin in the germ track 

 may be the result of the differentiation of the germ cells rather than its 

 cause, the differentiation at this stage being primarily a physiological 



B 



FIG. 158. 



A, chromatin diminution in Ascaris megalocephdLa. The second cleavage mitosis is in 

 progress: all the chromatin is retained in the upper blastomere, from which the germ 

 cells are to arise, whereas chromosome diminution occurs in the lower blastomere, which 

 is to give rise to the somatic cells. (After Boveri.) B, third nuclear division in the yet 

 unsegmented egg of Chironomus confinis showing the early setting aside of the primitive 

 germ cells at the lower end. (After Hasper.) 



(metabolic) one. He refers to certain later researches of Boveri (1910), 

 which apparently show that "the occurrence or non-occurrence of chro- 

 matin diminution in a nucleus depends, not upon its qualitative con- 

 stitution, but upon its cytoplasmic environment." From this it is 

 concluded that "the 'germ path' is a feature of the cytoplasm, and the 

 cytoplasm is not, properly speaking, a part of the germ-plasm at all, 

 but represents the soma of the cell" (p. 327). 



In support of this conclusion we may cite, as does Child, those cases 

 among insects (Hasper on Chironomus, 1911 ; Hegner on Miastor, 1912, 

 1914) and copepods (Haecker 1897, 1902; Amma 1911) in which the 

 substance of the future germ cells may be distinguished very early in 

 the embryogeny, even in the undivided egg, either as a visibly differen- 



