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INFLUENCE OF ENVIRONMENT 



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 AmpTiioxus. 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 gastrulae arising from such 

 forms as the last. (From Wilson.) 



