FACTORS IN ONTOGENY 



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FIG. 157. A, Hybrid larva (Sphcerechinus $ and Echinus i), front view; B, the same 

 from side view; C, hybrid larva, Sphcerechinus $ (nonnucleated egg formation; 

 and Echinus , of the type; D, the same larva in side view. (After Boveri.) 



19 



