164 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Echinocardium eggs with Echinus sperm. The reverse cross is sterile, 

 for the spermatozoon of Echinocardium entering an Echinus Qg^ pro- 

 duces a cytolytic action (leading to the formation of a fertilization- 

 membrane), but cannot check it when it goes too far. 



The larva of Echinocardium differs from that of Echinus (1) in 

 possessing an aboral spike supported by a complicated skeleton, whilst 

 at the aboral pole of the Echinus nothing of this kind is to be seen ; 

 (2) in possessing " latticed " bars instead of single rods as supports for 

 the post-oral arms ; (3) in possessing well-developed recurrent rods 

 instead of only vestiges of such rods ; (4) in possessing brownish-red 

 instead of orange-red pigment ; and (5) in its more rapid development. 



The hybrid produced by fertilizing the eggs of Echinocardium with 

 the sperm of Echinus follows the mother in the character and distribu- 

 tion of the pigment ; it is much smaller than the larvse of either parent ; 

 it almost always follows the father in the total absence of the aboral 

 spike and of its supporting skeleton, since in only one hybrid out of 

 the hundreds examined was the aboral spike formed. In the skeleton 

 of the post-oral arms the hybrid may be of the paternal type, of the 

 maternal type, or of an intermediate character. In the inbending of 

 the aboral ends of the body-rods the hybrid follows the father. 



Hybridization of Echinus Species.* — G. Debaisieux has made ex- 

 periments on the hyljridization of three species of Echinus — E. miliar is ^ 

 E. esculentus, and E. acutus. He concentrated his attention on three 

 characters : — (1) the posterior epaulettes, which are present in E. escu- 

 lentus and E. acutus, absent in E. miliar is ; (2) the posterior pedicellaria, 

 which is present in E. escidentus and E. acutus, absent in E. miliaris ; 

 and (3) the green pigment, which is absent in E. escidentus and E. 

 acutus, present in E. miliaris. 



He obtained the four possible hybrids : — M ? x E <5 : E ? M <^ ; 

 M 9 X A c5 ; A ? and M 6 . The hereditary relations of the three 

 characters studied were as follows: — !. The posterior epaulettes were 

 present in all the larvae of the four kinds of hybrids. 2. The posterior 

 pedicellaria is to be found in the following hybrids : M ? x A <? , 

 A? xM<?,E9 xMc5,and probably also in M ? and E 6 . But it 

 may be absent in individual larvae. ?>. The green pigment is never 

 transmitted to the larvse in any of the four kinds of hybrids. 



The author points out that m these crossings of three species, there 

 is not exclusively maternal or paternal inheritance. The hybrids inherit 

 simultaneously from the paternal and the maternal influence. But this 

 does not express all the results obtained, for certain characters are 

 always absent or always present in all hybrids, and the paternal or 

 maternal origin of the characters does not influence their transmission to 

 descendants. It seems as if certain characters were dominant, and 

 others recessive. The dominant characters are the presence of posterior 

 epaulettes and of posterior pedicellaria. They are always transmitted, 

 either through the father or through the mother. The green pigment, 



* Quart. Journ. Micr, Sci., Iviii. (1912) pp. 325-35 (1 pi.). 



