1900.] on Facts of Inheritance. 351 



develop into green fly in the summer ; and cases like liver-flukes, 

 where an animal is both mother and father to its offspring. Apart 

 from these exceptions the inheritance does at the start consist of 

 maternal and paternal contributions in intimate and orderly union. 



Prof. E. B. Wilson states the general opinion of experts somewhat 

 as follows : — As the ovum is much the larger, it is believed to furnish 

 the initial capital — including it may be a legacy of food-yolk— -for 

 the early development of the embryo. From both parents alike comes 

 the inherited organisation which has its seat (according to many) in 

 the readily stainable (chromatin) rods of the nuclei. From the father 

 comes a little hody (the centrosome) which organises the machinery of 

 division by which the egg splits up, and distributes the dual inherit- 

 ance equally between the daughter-cells. 



Recent discoveries have shown that the paternal and maternal 

 contributions which come together in fertilisation, are for several 

 divisions at least exactly divided among the daughter cells, thus con- 

 firming a prophecy which Huxley made in 1878 : " It is conceivable, 

 and indeed probable, that every part of the adult contains molecules 

 derived both from the male and from the female parent ; and that, 

 regarded as a mass of molecules, the entire organism may be compared 

 to a web of which the warp is derived from the female and the woof 

 from the male." " What has since been gained," Prof. Wilson says, 

 " is the knowledge that this web is to be sought in the chromatic 

 substance of the nuclei, and that the centrosome is the weaver at the 

 loom." 



In regard to these conclusions I wish to make three remarks, (a) 

 Although inheritance is dual, it is in quite as real a sense multiple, 

 from ancestors through parents, as we shall afterwards see. (b) 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 ourselves definitely to 

 the conclusion that the nuclei are the exclusive bearers of the heredi- 

 tary 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 inheritance 

 must be patent in the full-grown offspring, for hereditai-y resemblance 

 is often strangely unilateral, the characters of one parent being " pre- 

 potent " as we say, over those of another. 



