INFLUENCE OF ENVIRONMENT 



323 



upside down in the 2-cell stage, double headed 

 or double bodied embryos may result (Fig. 

 71 ) . In such cases each cleavage cell is said to 



Fig. 70. Dwarf and double embryos of Amphioxus. A, 

 isolated blastomeres of the 2-cell stage segmenting like an 

 entire egg. B, twin gastrulae from a single egg. C, double 

 cleavage resulting from partial separation of the first two 

 cleavage cells. D, E, F, double gastrulse arising from such 

 forms as the last. (From Wilson.) 



