2l6 



Heredity and Environment 





FIG. 77. HALF AND THREE-QUARTER EMBRYOS OF Styeia. np, nerve plate; 

 nt, nerve tube; E, eye; mch, mesenchyme; ms, muscle; ch, notochord. A, 

 right half-blastula which developed after the left half of the egg, A 3 B 3 , had 

 been killed. B, left half larva from the two left cells of the 4-cell stage, the 

 right cells, A Z B Z , having been killed. The muscle cells (stippled) occur 

 only on one side of the notochord. D, three-quarter larva, the left an- 

 terior cells having been killed. E, F, three-quarter larvae, the right pos- 

 terior cell B 3 having been killed. 



