THEIR SIGNIFICANCE IN HEREDITY. 371 



understand how any of the ancestral germ-plasms could be lost 

 during- such a course of development. 



Whichever view, the latter or the theory of the continuity of 

 the germ-plasm, be correct, in either case the male germ-cells of 

 the young animal must contain the same germ-plasm as that 

 which existed in the fertilized maternal egg, that is to say, they 

 must contain all the ancestral germ- plasms of the father and the 

 mother. Here therefore a reduction must occur, for otherwise the 

 number of ancestral germ-plasms would be increased by one half at 

 every fertilization. The egg-cell would furnish |, but the sperm- 

 cell | of the total quantity of germ-plasm present in the germ- 

 cells of the parents. But there is no reason for believing that 

 the reduction of germ-plasm in the sperm-cell must proceed in 

 precisely the same way as in the egg-cell, viz. by the expulsion 

 of a polar body. On the contrary, the processes of spermato- 

 genesis are so remarkably different from those of ovogenesis that 

 we may expect to find that reduction is also brought about in a 

 different manner. 



The egg-cell does not expel the superfluous ancestral germ- 

 plasms until the end of its development, and in a form which 

 induces the destruction of the separated portion. This is certainly 

 remarkable, for germ-plasm is a most important substance, and 

 although it seems to be wasted in the production of enormous 

 quantities of sperm- and egg-cells, such waste is only apparent, 

 and is in reality the means which renders the species capable of 

 existence. It may perhaps be possible to prove that in this case 

 also the waste is only apparent. Such proof would bo forthcoming 

 if it could be shown that the means by which reduction is brought 

 about in eggs is advantageous, and therefore also, ceteris paribu-s, 

 necessary. We see that everywhere, as far as our observation ex- 

 tends, the useful is also the actual, unless indeed it is impossible 

 of attainment or can only be attained by the aid of processes which 

 are injurious to the species. And if it be asked why germ-plasm 

 is wasted in the maturation of egg-cells, the following may per- 

 haps be a satisfactory answer. 



Let us suppose that the necessary reduction of the germ-plasm 

 does not take place by the separation of the second polar body, but 

 that it happens during the first division of the first primitive-germ- 

 cell which is found in the embryo, so that the two first egg-cells 



B b 2 



