FACTS AND FACTORS OF DEVELOPMENT 19 



ginning of the individual's existence. And yet 

 in all cases the new individual is always dis- 

 tinguishable from the body of the mother since 

 there is no protoplasmic connection between 

 the two. In mammals generally, including 

 also the human species, not a strand of proto- 

 plasm, not a nerve fiber, not a blood vessel 

 passes over from the mother to the embryo; 

 the latter is from the moment of fertilization 

 onward a distinct individual with particular 

 individual characteristics, and this is just as 

 true of viviparous animals in which the egg 

 undergoes a part of its development within 

 the body of the mother as it is of oviparous 

 ones in which the eggs are laid before devel- 

 opment begins. 



The fertilized egg of a star-fish, or frog, or 

 man is not a different individual from the 

 adult form into which it develops, rather it is 

 a star-fish, a frog, or a human being in the one- 

 celled stage. This fertilized egg fuses with 

 no other cells, it takes into itself no living 

 substance, but manufactures its own proto- 

 plasm from food substances; it receives food 

 and oxygen from without and it gives out 



