On Mendelian Dominance. 



171 



To turn to a more familiar example of the working out of this 

 hypothesis, we may note the inheritance of hair and eye pigment in 

 the human species. Young children who are the result of a cross 

 between a blond and a brunette usually are blonds but develop more 

 hair and eye pigments later in life. In the children of two brunettes 

 hair and eye pigments appear strongly in infancy. 



It occurred to me that a phenomenon of the same nature might 

 be observed in the development ot the larvae of the two Pacific Coast 

 sea urchins (Strongylocentrotus purpuratus and 8. franciscanus] and 



Fig. 1. 



Fig. 2. 



Fig. 3. 



their hybrids. In preparing the cultures much the same precautions 

 against contamination with the wrong sperm were used as last year 1 ), 

 viz: a pipette was not used a second time until after it had been 

 cleaned with fresh water and dried. The eggs of but one female 

 of each species were used for purposes of comparison. The cultures 

 of one set were all started at the same time. I did not study the 

 FQ x PC? hybrids because such larvae, with few exceptions, are 

 pathological. As soon as the blastulae came to the surface of the 

 water they were pipetted off and put into a finger bowl containing 

 50 cc. of sea water. About forty-eight hours after fertilization 



S. 354. 



LOEB, J., KING, W. 0. R., and MOORE, A. R., Arch. f. Entw.-Mech. Bd. 29. 



