62 THE BIOLOGICAL PROBLEM OF TO-DAY 



cells isolated from the two, four, or eight-celled 

 stage of the segmenting egg. 



Results which Chabry and I gained by destroy- 

 ing, by puncture, one of the first two segmentation 

 spheres, assist the present argument. Although 

 one-half of the mass had been destroyed, Chabry 

 obtained, in the case of an ascidian, and I obtained, 

 in the common frog, embryos with notochord and 

 nerve-plate. These developed directly and normally, 

 although, in the case of the frog, there was a slight 

 defect at the ventral posterior part of the body, 

 where the arrested protoplasmic mass came to lie. 



All these experiments show that the first two 

 (and in some cases the first four) results of division 

 can assume a quite different bearing as regards 

 their function in the mechanical building of the 

 embryo, according to whether they remain bound 

 with each other into a whole or are separated and 

 develop by themselves. In the former case, each 

 forms only one-half (in some cases only a fourth) of 

 the whole. In the latter case, each by itself pro- 

 duces the whole. The half and the whole, then, of 

 the first cleavage-cells are identical in real nature, 

 and, according to the circumstances, can develop, 

 now in this way, now in that. 



Even if Weismann were to admit the correctness 

 of these experiments, perhaps he would not con- 

 sider that they contradicted his theory of the germ- 

 plasm and the segregation of the hereditary mass, 

 but would make a supplemental hypothesis, which, 

 from the spirit of his theory, could be none other 

 than this : each of the first cleavage - cells, in 



