374 EXPERIMENTAL STUDY OF INHERITANCE 



Mendelism in Relation to Ancestral Inheritance. — It may 



be that the conception of ancestral inheritance and the conception 

 of segregate parental inheritance apply to different sets of 

 cases. 



1. At one extreme we may perhaps place cases of sterility, 

 where the fertilised egg-cell fails to develop, owing perhaps to 

 mutual incompatibility between the paternal and maternal 

 contributions. " The sterility of distinct species when crossed 

 is probably due to the confusion and disruption of the systems 

 of forces in the pronuclei of the germ-cells by antagonising 

 ancestral stimuli" (Dendy, 1903). 



2. It is possible that in some cases where a spermatozoon 

 enters an e^^ it fulfils one of its functions — acting as a liberating 

 stimulus prompting the egg to develop — and yet does not fulfil 

 its other function of contributing half of the inheritance. It is 

 possible that it is sometimes only the egg-nucleus which develops. 

 This possibility is suggested by some of the results of experi- 

 mental embryology — e.g. that an egg may develop with only a 

 sperm-nucleus (merogony), or with only its own nucleus (artificial 

 parthenogenesis ) . 



3. Dendy suggests that those remarkable abnormal insects 

 (see Darwin, Variation of Animals and Plants under Domestication, 

 vol. ii. p. 394), in which one-half or one-quarter of the body is 

 like that of the male and the other half or three-quarters like 

 that of the female, may be due to an inadequate blending of the 

 male and female nuclei. " They may separate completely at 

 the first or at some subsequent division of the segmentation 

 nucleus, and thereafter each may control a certain fraction of 

 the developing organism, yielding a lop-sided result." 



4. The maternal and paternal contributions may remain 

 together in the development of the body, though one is dominant, 

 but they may be dissociated in the formation of the germ-cells, 

 so that two sets of germ-cells result .(Mendelian inheritance). 



5. The maternal and paternal contributions may find equal 



