REPRODUCTION. 673 



cell, the male constituent is removed ; and, similarly, that in 

 the extrusion of the polar body from the developing male 

 cell, the female constituent is removed. 



The next point to be considered is the functional relation 

 between two coalescing gametes. When they are externally 

 similar, there is no reason to suppose that the two gametes 

 are functionally different. For example, when two piano- 

 gametes of Ulothrix or Acetabularia coalesce, there is no 

 ground for the supposition that one of the planogametes is 

 fertilised by, or fertilises, the other. They are, as we believe, 

 qualitatively different, but, in the sexual process, they are 

 functionally alike ; each is complementary to the other, and 

 each transmits to the offspring the characteristics of the 

 parent individual. 



In the case of two corresponding gametes which are ex- 

 ternally different, for instance an oosphere and an anthero- 

 zoid, it is customary to regard the passive gamete as being 

 the female, and the active as being the male. And not only 

 so, but the sexual process is termed fertilisation, that is to 

 say, it consists in the fertilisation of the female by the male 

 gamete. This view involves the assumption of a considerable 

 functional difference between the gametes ; namely, that it 

 is from the female gamete that the embryo is actually de- 

 veloped, whilst the male gamete simply stimulates the female 

 gamete to development. This is the assumption which under- 

 lies Brooks' theory of the sexual process to which allusion has 

 been already made (p. 656). 



Careful consideration of the facts of the sexual process 

 shews, however, that this assumption cannot be admitted. 

 The fact which seems to give it most support, the fact of the 

 difference in mass between an antherozoid and an oosphere, 

 is really of no weight. It may be urged, on account of the 

 difference of mass, that the oosphere contributes more to the 

 embryo than does the antherozoid. But it must be re- 

 membered that the difference in mass between an oosphere 

 and an antherozoid depends mainly upon the cytoplasm ; 

 hence, although it is true that the antherozoid contributes but 

 little cytoplasm in the sexual process, it contributes probably 



V. 43 



