Chemical Basis of Genus and Species 49 



If such heterogeneous hybridizations are carried out, 

 two striking results are obtained. The one is that 



Fig. 1. Five-days-old larvae from a sea urchin (Strongy- 

 locentrotus purpuratus) 9 and a starfish (Asterias) d 1 . 

 (Front view.) 



the resulting larva has only maternal characteristics 

 (Figs. I and 2) , as if the sperm had contributed no he- 



Fig. 2. Five-days-old larvae of Strongylocentrotus purpur- 

 atus produced by artificial parthenogenesis. (Side view.) 

 The larvae in Figs. 1 and 2 are identical in appearance, 

 proving that heterogeneous hybridization leads to a larva 

 with purely maternal characters. 



reditary material to the developing embryo. This result 

 could not have been predicted, for if we fertilize the 

 egg of the same Californian sea urchin, Strongylocen- 

 trotus purpuratus, with the sperm of a very closely 



