400 THE HEREDITARY FACTORS AND DIFFERENTIATION 



plane, or the plane of the egg-axis, and both the resulting two 

 blastomeres contain a portion of the original vegetative-pole cyto- 

 plasm ; it is further found that both retain the entire chromosomes. ^ 

 Each of these two blastomeres then behaves like the single blasto- 

 mere of the 2-cell stage which contains the vegetative-pole cyto- 



Fig. 193 



Results of centrifuging the egg of Ascaris. Above: left, an uncleaved egg after 

 centrifuging ; centre and right, resultant division into two similar cells (plus a 

 small centripetal mass containing yolk). Below: the behaviour of the chromo- 

 somes in centrifuged eggs ; left, no diminution of chromosomes in the 2-cell 

 stage ; right, diminution of the chromosomes in both of the two upper cells. (After 

 Hogue, from Morgan, Experimental Embryology, Columbia University Press, 

 1927; modified.) 



plasm in normal development, and the embryos resulting from 

 such treatment are double monsters (fig. 193; and see p. loi). 



The conditions controlling the retention of entire chromosomes 

 in the blastomeres of Ascaris, therefore, reside not in the nuclei but 

 in the cytoplasm. The cytoplasm produces a situation to which the 



^ Boveri and Hogue, 1909. 



