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



years and unaffected by this variation. As we have said, this has been the case, and 

 the inheritance in 1912 in these forms has been quite the same as in former years, 

 that is as far as the hmited characters furnished by these species allow of our judging. 



That temperatui-e may play a part in inheritance of larval characters would seem 

 to be borne out by the work of Vernon (96), Doncaster (21), and Herbst (39). 

 Vernon, working at Naples in 1900, found that the inheritance in hybrids between 

 Strongylocenti'otus and Sjjhcerechimis was different according to the time of season 

 at which the cross was made. In the spring the hybrid larvee resembled Strongi/lo- 

 centrotus, while if the cross was made in the summer they resembled Sphcerechinus. 

 The breeding period of Strongylocentrotus reaches its maximum in the spring, and 

 therefore the eggs and sperm are riper at this time than in the summer, and from 

 this Vernon concluded that the dominance of the one form over the other was 

 controlled by the relative ripeness of the sex cells. 



Doncaster, following up this work, found that it was possible to get the hybrids 

 resembling Spluerechinus in the spring, just as well as those resembling Strovgy- 

 locentrot'us, by heating up the water ; that it was the difference of temperature 

 between spring and summer which determined the character of the inheritance, 

 turning it either to the Strongylocentrotus or the S-phcerechinus side. The rather 

 extended breeding periods of the Echinoderms at Naples renders it easy to make 

 observations on the relative ripeness of the sexual products. At Plymouth it is 

 impossible to make similar observations on account of the short breeding season. As 

 we have seen in Section 8 (p. 299), with our forms it makes no difference whether 

 the cross is made at the beginning, middle, or end of the bi*eeding season ; the 

 characters of the cross always remain the same. 



Herbst (39) made the crosses Sphcerechinus $ X Strongylocentrotus $ and Sphcer- 

 echinus ? X Echinus $ with a view of investigating the seasonal variation of 

 inheritance described by Vernon. Although Doncaster's paper had appeared 

 several years previous to this, Herbst was unfxmiliar with it till he had concluded 

 his experiments. His work is therefore in large part a repetition of Doncaster's 

 work on a larger scale. He raised his hybrids under different temperature con- 

 ditions, and found that, in the warmth, on an average they were more like the mother 

 {SpJice7'echinus) than was the case when they were grown in the cold. Tliis result 

 was not clearly marked, however, as he found that pure Sphcerecliinus were also 

 developed to a greater degree in the warmth. Again, all characters were not 

 maternal in the warm-bred hybrids. 



Herbst considers Vernon's seasonal change as not due to relative ripeness, but to : 



(1) Temperature. 



(2) An unknown factor, of varying intensity at different seasons. 



Herbst thinks that Weismann's position, that the characters of the future 

 individual are determined at the time of fertilization, is in general true, but he also 



