ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 339 



It remains now to discuss the causes and meaning of the two chief results of the 

 work, namely the invariable maternal inheritance of the late larval characters during 

 three successive years and the remarkable change in this rule in the fourth year. 



We will consider first the transmission of characters through the female germ cells 

 alone. During the seasons 1909-11 hybrids between the three species of Echinus 

 always inherited the posterior ciliated epaulettes and the green pigment masses of the 

 late larvfe through the female parent. This is unlike the usual case of inheritance 

 according to Mendelian laws, when all the F, hybrids are alike, if the parental forms 

 are homozygous. The F, hybrids may be intermediate or may resemble one or other 

 of the parental forms, but in the latter case it makes no dift'erence whether the 

 dominating character comes in through one sex or the other. It must, however, be 

 remembered that our crosses were made between distinct species. Goldschmidt 

 (32, p. 324) observes that, whereas in crosses between the varieties of a species the 

 reciprocals are almost always alike, in species hybrids (" Artbastarde") they are 

 often different from one another, as for instance the well-known case of hybrids 

 between the horse and ass.* 



Parallel cases possibly similar to the above are shown by : — 



(1) Echinoderm crosses. 



(2) Crosses between (Unothera biennis and (^. muricata. Reciprocal hybrids 

 between these forms differ from one another and from their parents. The characters 

 of the hybi'ids do not alter in four generations [HuGO DE Vries (99)]. 



G^. biennis $ X (E. muricata $ resemble CE. muricata. 

 (E. muricata % X (E. biennis $ resemble (i'. biennis. 

 There is thus an inheritance through the male germ cells. 



(3) Kammerer (44) found a different dominance in the two reciprocals of a cross, 

 which he called " sexual prepotency." When a female midwife toad, which inherited 

 artificially changed breeding instincts, was crossed with a normal male, the Fj offspring 

 were normal. In the reciprocal the Fi generation consisted of animals with changed 

 breeding habits. Here again, therefore, the inheritance was through the male germ 

 cells alone. 



(4) Przibram (76) in the Mantidce ; if artificial fertilization was effected between 

 Sphodromantis bioculata $ X Mantis religiosa $ the offspring were all Sphodro- 

 mantis, only one of which reached the imago stage. This was a $ and was crossed 

 with a Sphodromantis $ . The offspring were Sphodromantis. There was thus no 

 segregation. Przibram suggests that it is a case of pseudogamy as in Kupelwieser's 

 (48 and 49) experiments. As he did not make the reciprocal cross, this case cannot 

 strictly be compared with ours. 



A number of other cases are known of reciprocals being unlike. 



* See also Darwin, 'Animals and Plants under Domestication,' 1890, 2nd Edit., p. 16. 



2x2 



