GENEOLOGICAL. 405 



egg-cell in which two organisations are subtly 

 mingled. We have already referred to the inter- 

 esting fact that the partition of paternal and mater- 

 nal chromatin-contributions between the daughter 

 cells of the segmenting ovum can be demonstrated in 

 early stages of development. 



In regard to this fact of dual inheritance, three 

 saving-clauses are suggested by recent researches. 



(a) Although inheritance is dual, it is in quite as 

 real a sense multiple, from ancestors through- parents, 

 as we shall afterwards see. (&) If Loeb is able to 

 induce artificial parthenogenesis in sea-urchins' eggs 

 exposed for a couple of hours to sea-water to which 

 some magnesium chloride has been added ; if Delage 

 is able to fertilise and to rear normal larvae from 

 non-nucleated ovum-fragments of sea-urchin, worm 

 and mollusc, we should be chary of committing our- 

 selves definitely to the conclusion that the nuclei are 

 the exclusive bearers of the hereditary qualities, or 

 that both must be present in all cases. Further- 

 more, the fact that an ovum without any sperm- 

 nucleus, or an ovum-fragment without any but a 

 sperm-nucleus, can develop into a normal larva points 

 to the conclusion, probable also on other grounds, 

 that each germ-cell, whether ovum or spermatozoon, 

 bears a complete equipment of hereditary qualities. 

 (c) It must be carefully observed that our second 

 fact does not imply that the dual nature of inherit- 

 ance must be patent in the full-grown offspring, 

 for hereditary resemblance is often strangely uni- 

 lateral, the characters of one parent being " pre- 

 potent " as we say, over those of another. 



(III.) Although specific inheritance tends to be 

 approximately complete, there are many degrees in 

 the completeness with which an inheritance is ex- 



