CRITIQUE OF THE ROUX-WEISMANN THEORY 



409 



the missing half \iy a peculiar process, related to regeneration, which 

 Roux designated as post-generation. Later studies showed that an 

 isolated blastomere is able to give rise to a complete embryo in manv 

 other animals, sometimes developing in its earlier stages as though 



E 



Fig. 185. — Dwarf and double embryos of Amphioxus. 

 A. Isolated blastomere of the two-cell stage segmenting like an entire egg Kef. Fig. 183. />>). 

 B. Twin gastrulas from a" single egg. C. Double cleavage resulting from the partial separation, 

 by shaking, of the blastomeres of the two-cell stage. D.E.F. Double gastrulas arising from such 

 forms as the last. 



still forming part of a complete embryo (** partial development"), 

 but in other cases developing directly into a complete dwarf embryo, 

 as if it were an ^g% of diminished size. In 1891 Driesch w^is ab^e 

 to follow out the development of isolated blastomeres of sea-nrchin 



