THE WAY LIFE BEGINS 31 



of the vertebrate animals on the earth might be compared 

 to a long road in which the fish branch off very early, the frogs 

 a little later, and then the birds take their separate way. 

 Mammals, like the rabbit, keep on the main road until 

 their time comes to turn aside. Finally the parting of the 

 ways comes for the higher apes and man. 



Biological science confirms in a thousand ways this concep- 

 tion of a long road with its many branchings, or a great tree 

 with its forking limbs at higher and higher levels. The 

 higher mammals are the terminal points on a great trunk 

 line of life. 



If one keeps in mind an image of this nature, the similarity 

 in the methods of animal reproduction will be understood. 

 It is to be expected that, on the whole, animals resembling 

 one another will have the same modes of development from 

 the egg to adult, and that there will be a marked tendency for 

 the higher forms to repeat, in the growth of the embryo, the 

 steps that are taken in forming the embryos of the animals 

 below them. The process in general is one of adding some- 

 thing new to an old pattern, rather than that of getting up a 

 new pattern for each level of advancement in organic life. 



