CREATION BY EVOLUTION 



which their parents passed; after that, and then only, does the 

 effect of the black environment begin to tell on them, for the 

 yellow spots begin to diminish in size/ 



The young forms termed larvae, which by their structure 

 and habits repeat ancestral conditions, live freely in the 

 world and earn their own living. The most familiar example 

 of a larva is the tadpole of the frog, which, by its gills and 

 tail recalls the fish-like ancestors of the frogs. There is 

 another type of young animal which is known as an embryo 

 (Greek 8v (8|i), in, ^Qijeiv, grow). This type, during its 

 development, is sheltered and fed either within an egg shell 

 or in the womb of the mother. A good example of this 

 type is the chicken, of which the greater part of the develop- 

 ment is completed within the egg shell. The young form in 

 this type derives its food from the yolk in the egg, which it 

 slowly digests as it grows, and from the "white," or albu- 

 men. Another variety of embryo is sheltered within the 

 womb of the mother and obtains all its nourishment from 

 the maternal blood. The embryos of all the higher warm- 

 blooded mammals, such as those of dogs, horses, and cattle, 

 as well as the human embryo, are of this kind. 



Now let us consider how the embryonic and the larval 

 types of development are related to one another. Was the 

 original form of development embryonic or larval? 



When we closely examine the life histories of animals we 

 discover that there is an embryonic and a larval phase in all, 

 though these phases are of extremely different lengths in 

 different animals. No animal deposits naked eggs; an egg- 

 shell, though it may be thin and elastic, is always formed, 

 and the egg always includes some yolk, so that there is 

 always a period during which the young animal develops as 



^ All biologists are not agreed as to the sufficiency of the evidence for the 

 inheritance of acquired characters. — Ed. 



[54] 



