2 EVOLUTION AND ANIMAL LIFE 



that something which was previously hidden is now brought to 

 light. This leads naturally to the philosophic suggestion that 

 whatever is evolved must be previously involved. This may 

 be true as a matter of words, but not necessarily so as a matter 

 of fact, unless we reduce these words to the simple meaning 

 that the actual now must have been the possible before; what- 

 ever actually takes place was a possibility before it happened. 



The word evolution, then, belongs to philosophy rather than 

 to science. In the philosophy of nature the idea that present 

 conditions are brought about through unrolling or unveiling 

 has had a long existence. The word evolution has been fre- 

 quently applied to the process of growth and maturity of the 

 individual animal or plant, and again to the process of deriva- 

 tion of species from ancestral organisms, and again to the pro- 

 gressive changes in the forms of inorganic bodies, as planets 

 or mountains. Each one of these meanings is essentially dis- 

 tinct from the others, and each is distinct from the theory 

 of evolution which existed in the dawn of biological science. 

 When men first began to notice the changes in the animal 

 embryo, through which, from the formless egg, little by little, 

 the individual was built up, becoming at each stage of the 

 process larger, more specialized, and more like the parent 

 from which it sprang, it was natural to regard this process as 

 an unrolling. It was natural, too, to suppose that the egg 

 was not really formless, but that the beginnings of each part 

 of the final organism existed within it in fact, if we could 

 see them. Hence evolution took the form of a theory of 

 encasement. Men imagined that the egg of the chicken con- 

 tained a minute chicken, and that within this chicken were 

 the germs of the eggs the future hen would bear; and again, 

 that encased within each of these eggs was an endless series of 

 the eggs and chickens of all the future. In like fashion, men 

 conceived that in the small human egg were the bodies and 

 embryos of countless future generations. In some theories, 

 this idea of encasement was applied not to the egg, but to the 

 male germ, the homunculus or minute man in whom the gener- 

 ations of the future were enfolded and from which they un- 

 rolled. 



The perfection of the microscope as an instrument of pre- 

 cision did not verify these theories of encasement. The egg 

 still appeared essentially formless, a mass of undifferentiated 



