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, fi^om ancestors through parents, 

 as we shall afterwards see. (h) 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, ivhether ovum or spermatozoon, 

 hears a C07nplete 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 he 

 approximately complete, there are many degrees in 

 the completeness with which an inheritance is ex- 



