64 Heredity and En genie s 



The egg or larger gamete (the so-called macro-gamete) 

 in all animals is non-motile and contains a relatively large 

 anu)unt of reserve food material for the maintenance of the 

 dc\'eloping embryo. This reser\-e food material it is the 

 function of the mother to supply. In the case of some 

 animals, for example flatworms and mollusks, the food 

 supph' of the embryo is not stored in the egg cell itself, but 

 in other cells associated with it, and which break dowm and 

 suppl\- nourishment to the developing embryo derived from 

 the fertilized egg. Again, as in the mammals, the embryo 

 mav derive its nourishment largely from the maternal 

 tissues, the embryo remaining like a parasite within the 

 maternal body during its growth, feeding by absorption. 

 But in all cases alike the mother supplies the larger gamete 

 and the food material necessary to carry the zygote through 

 its embryonic stages. The father, on the other hand, 

 furnishes the bare hereditary equipment of a gamete, with 

 the motor apparatus necessary to bring it into contact with 

 the egg cell, but without food for the developing embryo pro- 

 duced by fertilization. The gamete furnished by the father 

 is therefore the smaller gamete, the so-called micro-gamete. 



From the standpoint of metabolism, the female is the 

 more advanced condition; the female performs the larger 

 function, doing all that the male does in furnishing the 

 material basis of heredit}' (a gamete), and in addition 

 supplying food for the embryo. As regards the reproduc- 

 tive function, the female is the ecjuivalent of the male 

 organism, plus an additional function, that of supplying 

 the embryo with food. When we come to consider the 

 structural basis of sex, we find reasons for thinking that 

 here, too, the female individual is the equivalent of the 

 male plus an additional element. The conclusion has very 



