50 THE PHYSICAL BASIS OF INHERITANCE 



several effect entrance at once, abnormalities usually result. 

 In the mature ovum there is no centrosome ; if it was originally 

 present, it disappears. The spermatozoon, however, intro- 

 duces, along with its nucleus, its centrosome, and this divides 

 into two. The two centrosomes appear to take an active part 

 in the approximation and intimate apposition of the maternal 

 and paternal chromosomes, and in their subsequent partition 

 between the first two daughter-cells. 



Prof. E. B. Wilson states the general opinion of experts some- 

 what 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 most biologists) in the readily stainable 

 (chromatin) rods of the nuclei. From the father comes a little 

 body (the centrosome) which organises the machinery of division 

 by which the egg splits up, and distributes the dual inheritance 

 equally between the daughter-cells. 



Let us now proceed to expound four important theorems. 



I. In Ordinary Sexual Reproduction the Inheritance is 

 very precisely Dual or Biparental. — 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 confirming 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." 



After the paternal and maternal chromosomes have united, 



