CHAPTER IV 



FERTILIZATION OF THE OVUM 



" 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." HuxLEY. 1 



IN mitototic cell-division we have become acquainted with the 

 means by which, in all higher forms at least, not only the continuity 

 of life, but also the maintenance of the species, is effected; for through 

 this beautiful mechanism the cell hands on to its descendants an 

 exact duplicate of the idioplasm by which its own organization is 

 determined. As far as we can see from an a priori point of view there 

 is no reason why, barring accident, cell-division should not follow 

 cell-division in endless succession in the stream of life. It is possible, 

 indeed probable, that such may be the fact in some of the lower and 

 simpler forms of life where no form of sexual reproduction is known 

 to occur. In the vast majority of living forms, however, the series 

 of cell-divisions tends to run in cycles in each of which the energy 

 of division gradually comes to an end and is only restored by an 

 admixture of living matter derived from another cell. This operation, 

 known ^fertilization or fecundation, is the essence of sexual repro- 

 duction ; and in it we behold a process by which on the one hand 

 the energy of division is restored, and by which on the other hand 

 two independent lines of descent are blended into one. Why this 

 dual process should take place we are as yet unable to say, nor 

 do we know which of its two elements is to be regarded as the 

 primary and essential one. According to the older and more familiar 

 "dynamic" hypothesis, brought forward by Biitschli ('76) and Minot 

 ('77> '79) an d afterwards supported by such investigators as Engel- 

 mann, Hensen, Hertwig, and Maupas, the essential end of sexuality 

 is rejuvenescence, i.e. the restoration of the growth-energy and the 

 inauguration of a new cycle of cell-division. Maupas's celebrated 

 experiments on the conjugation of Infusoria, although not yet ade- 



1 Evolution, in Science and Culture, p. 296, from Rnc. Brit., 1878. 

 K 129 



