312 MESSRS C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



which had three tube-feet in each radius owed them to maternal influence, then this 

 character can be transmitted inde2:>endently of the larval characters, which were here 

 paternal. This would be parallel to the occasional cases where in one individual 

 the epaulettes were inherited from one parent and the green pigment from the other. 



Crosses between E. acutus and E. miliaris. 



1 . £J. acutus $ X E. miliaris $ — 



This cross gave, in the majority of cases, larvae with maternal characters. The 

 larvfe which metamorphosed produced Echini with one tube-foot in each radius, that 

 is to say, they inherited the maternal character (Plate 23, fig. 96). 



2. E. miliaris ? X E. acutus $ — 



All cultures of this cross gave larvae with paternal characters. In the majority of 

 cultures the Echini which metamorphosed had one tube-foot in each radius, which 

 shows a paternal inheritance (Plate 23, fig. 97). In one case, however, as mentioned 

 above, there was an ficJiinus with one terminal tube-foot and a single small tube-foot, 

 instead of a pair, in each radius. In another culture seventy-nine Echini had the 

 paternal character (absence of the paired tube-feet), one had the maternal character 

 (presence of the paired tube-feet), and five had, at metamorphosis, rudiments of the 

 paired tube-feet, being thus intermediate. 



12. Experimental Contkol of Dominance. 



The problem of the factors influencing the dominance of one form over another in 

 Echinoderm hybi"ids has been attacked by several investigators. Vernon (96) 

 showed that, with hybrids between Strong ijlocentrotus and Sphcerechinus at Naples, 

 there was a seasonal change in dominance. In the spring the hybrids resembled 

 Strongylocpntrotus, while in summer they resembled SphcBrechitius. He concluded 

 that this seasonal change in " prepotency " was due to the relative maturity of the 

 sexual products, for Strongylocentrotus is most mature in spring and least so in 

 summer. Doncaster (21) confirmed the seasonal change in dominance, which 

 Vernon had found, but he considered that Vernon had been mistaken in attributing 

 it to the relative ripeness of the germ cells used to make the cross. By raising the 

 temperature at which the larvae were reared, in the spring, he caused them to assume 

 the summer form. Thus the higher temperature of the summer months was probably 

 the cause of the dominance of Sphcerechinus chai'acters at that season. 



Herbst.(39) produced a maternal dominance in hybrids, by causing the com- 

 mencement of artificial parthenogenesis in Sphcerechinus eggs, and then fertilizing 

 them with Strongylocentrotus sperm. The greatest eff'ect was produced when 

 fertilization took place at the time when the egg nucleus had reached its maximum 

 size. For this reason Herbst attributed the maternal dominance to the relatively 

 large size of the egg nucleus as compared with the sperm nucleus at the moment of 

 their union. 



