1911.] 



Studies in Heredity. 



401 



a dark red colour, those of the larva of Echinus are of a light red colour. In 

 this respect the hybrid agrees with the maternal parent It is right to add 

 that, out of all the hundreds of hybrid larvae reared, I found one solitary case 

 where the aboral spike had been developed ; evidently, therefore, the paternal 

 influence is not equally strong in all hybrids, a conclusion which is supported 

 by the very varying extent to which lattice-work is developed in the arms of 

 the hybrid. 



Numerous attempts were made to fertilise the eggs of Echinus esculentus 

 with the sperm of Echinocardium corclatum, in order to obtain the reciprocal 

 hybrid. At first it was thought that success had been attained, for a number 



Fig. 3.— A Hybrid derived from an Egg of Echinocardium cordatum, fertilised with the 

 Sperm of Echinus esculentus, Six Days old, viewed from the Dorsal Surface. 

 a.L, an tero- lateral arm ; b.s., body rod ; cos., coelornic sac ; p.o., post-oral arm. 

 of eggs developed into larvae which showed purely maternal characters. 

 When, however, the precaution was taken of thoroughly sterilising the sea- 

 water in which the fertilisation was made, by heating it to 70° C. and 

 allowing it to cool, none of the eggs developed. 



Further, when the eggs of Echinus esculentus were allowed to lie in clean 

 sea-water, without the addition of any spermatozoa, a small proportion 

 developed. It is clear therefore that ordinary sea- water, in the summer 

 time, contains enough spermatozoa to cause some of the eggs to develop, a 

 result not to be wondered at when we consider the abundance of Echinus 

 esculentus, and the number of males which must be discharging their 



