236 THE PERPETUATION OF ADAPTATIONS 



it would mean, if taken at its face value, that by re-combination 

 of the differences already present in the first living mate- 

 rial, all of the higher animals and plants were foreordained. 

 In some way, therefore, the germ plasm must have changed. 

 We have then the alternatives. Is there some internal, initial or 

 driving impulse that has led to the process of evolution? Or 

 has the environment brought about changes in the germ plasm? 

 We can only reply that the assumption of an internal force puts 

 the problem beyond the field of scientific explanation. On the 

 other hand, there is a small amount of evidence, very incomplete 

 and insufficient at present, to show that changes in the environ- 

 ment reach through thesoma and modify the germinal material" 

 (T. H. Morgan, Heredity and Sex, pp. 17-18). 



The origin of adaptations thus, specifically in our group of 

 Crustacea, is still difficult to explain. Some advance of a sure 

 kind has nevertheless been made. We know that a funda- 

 mental property of protoplasm is its power to vary, to adapt 

 itself to changed conditions of environment. In higher animals 

 the somatic protoplasm certainly exhibits this property, and 

 there is no a priori reason why the germ plasm also should not 

 possess it. We know also that changes in one organ bring about 

 compensatory or regulating changes in others, and again there 

 is no a priori reason why the germ plasm should not partake 

 in this reaction. An adaptation in our Crustacea may have 

 originated as a useful mutation ; in the germ plasm, it may have 

 been present as a simple Mendelian characteristic, subject to seg- 

 regation during the maturation stages. Later it may have be- 

 come too deeply impressed in the germ plasm to undergo seg- 

 regation, and became a fundamental part of the racial plasm 

 no longer subject to extinction by natural selection, while the 

 environment remained the same. Such an origin, especially for 

 all of the variations in a present-day phylum, and in different 

 phyla, demands time. The history of the earth, as written in 

 modern geology, allows some hundred millions of years for 

 modern types to have evolved, and if seventy-five mutants of 

 a single species may be experimentally produced in seven years, 

 it is conceivable that 500,000 species of animals might have been 



