394 H. H. NEWMAN 



the latter come to be indistinguishable from Echinus chromo- 

 somes; yet the larvae are pure maternal in so far as they are any- 

 thing definite. In these wide 'crosses' it appears reasonable to 

 conclude that the foreign sperm at least assists in the initiation 

 of development, duplicating in a sense the role of partheno- 

 genetic agents. According to Loeb: ''The egg behaves exactly 

 as we should expect from the fact that the spermatozoon removes 

 only certain obstacles for the development of the egg, but does 

 not cause its development by carrying any activating enzyme." 



It may be concluded, then, that in Echinoidea crosses of 

 generic and family width exhibit paternal heredity, that when 

 Echinoids are 'crossed' with other classes or other phyla that 

 heredity is not concerned, but merely initiation of development. 

 The really interesting and critical phases of Echinoid hybridiza- 

 tion lie between these extremes: in crosses of subordinal, ordinal, 

 and subclass width, and there are, unfortunately, very few data 

 on this point. 



A cross of subordinal width was studied by Driesch and by 

 Herbst. Their results and conclusions are diametrically op- 

 posed; the former concluding that the hybrid larvae were purely 

 maternal and the latter that the paternal influence was seen in 

 several characters. More work is needed upon crosses of this 

 width. A cross of subclass width was made by McBride and 

 repeated by Fuchs with results quite different in the two cases, 

 and it seems certain from what these authors say that the larvae 

 are so few and so abnormal that little conclusive evidence as to 

 heredity is available. 



In conclusion it may he said that the results of hybridization ex- 

 periments of greater than interfamily width among the Echinoids 

 have been entirely inconclusive, and it would appear necessary to 

 transfer our attention to Teleost material if we wish for any approach 

 to a definite answer as to the question whether heterogenic hybrids 

 show paternal heredity or are merely parthenogenetic in character. 



