34 HEREDITY AND ENVIRONMENT 



chiefly nutritive in character. Careful studies 

 have shown that supposed "maternal impres- 

 sions" of the physical, mental, or emotional 

 conditions of the mother upon the unborn child 

 have no existence in fact, except in so far as 

 the quality of the mother's blood may be 

 changed and may affect the child. At no time, 

 whether before or after birth, is the mother 

 more than nurse to the child. Hereditary in- 

 fluences are transmitted only through the egg 

 cell and the sperm cell and these influences 

 are not affected by intra-uterine development. 

 The principles of heredity and development 

 are the same in oviparous and in viviparous 

 animals in fishes, frogs, birds and men. 



Summary. This is a very brief and incom- 

 plete statement of some of the important stages 

 or phases of the development of the body of 

 man or of any other vertebrate. In all cases 

 development begins with the fertilized egg 

 which contains none of the structures of the de- 

 veloped animal, though it may exhibit the 

 polarity and symmetry of the adult and may 

 also contain specific kinds of protoplasm which 

 will give rise to specific tissues or organs of 



