REPRODUCTION 



391 



the fusion within the egg of the nuclear material from the 

 two parents. 



A child inherits equally from the father and the mother. 

 This recognized fact may prove puzzling to the student, 

 who will be disposed to say that the paternal contribution 

 is infinitesimal compared with that derived from the 

 mother. Biologists have been led to the belief that the in- 

 herited traits, as these are commonly recognized, must be 

 associated with the nuclei of the germ-cells. The nuclear 

 material, as we can plainly see, comes equally from both 



FIG. 82. 1, A spermatozoon or male germ-cell highly magnified. 

 2, An ovum less highly magnified. It has a rather conspicuous envel- 

 ope, the zona pellucida. 3, An ovum which has been exposed to the 

 sperm, s, The half-nucleus derived from the head of a spermatozoon 

 which has entered the interior of the egg and will soon unite with the 

 half-nucleus already present. With the union of the two fertilization 

 will be accomplished. Two additional sperm-cells are arrested in the 

 capsule. 4, Two cells which have arisen by the cleavage of the fertil- 

 ized egg. They "are still within the old envelope. 5, The next or four- 

 cell stage. 



parents. A truth which needs particular insistence is the 

 following : that the growing embryo is not in the best sense 

 a part of the mother, but from the moment of fertilization 

 a new individual. The mother serves the child before 

 birth, much as she will later on, by giving it protection and 

 food. It will be appreciated that this view does not en- 





