CRUSTACEA AND MOLLUSCS 257 



of the many noses that are in a sense contained in the 

 fertilised ovum only one is developed and not several, 

 and what forces cause one property to be derived from 

 the father, another from the mother or an ancestor, are 

 questions involving general theories of heredity with 

 which we shall deal later. We will be content here to 

 establish the fact that there is a mechanism in the 

 fertilised ovum that builds up harmoniously the new 

 individual from the many characteristics it contains, 

 by always selecting one quality out of several equivalent 

 ones. 



The great value of amphimixis is, then, that it adds 

 new and different paternal qualities to those that the 

 new organism receives from the mother, so that it has 

 a choice, and has a greater variety in its composition 

 than it would have without amphimixis. It is true 

 that even parthenogenetic offspring do not entirely 

 resemble the mother, because each ovum contains 

 variations, and many of the mother's characteristics 

 appear slightly changed in her progeny. Nevertheless, 

 such offspring will be more uniform in structure than 

 others that suddenly receive a series of characteristics of 

 a totally different individual. 



For these the constant re-combination of characters 

 in the offspring is of the greatest value ; it gives a wider 

 field of operation to natural selection. It enormously 

 increases the adaptive capacity of the animals, and the 

 variations from which one animal would arise here, 

 and another there, are united in one individual. It is 

 due to amphimixis, therefore, that co-adaptations do not 

 need to be selected slowly and successively, but may 



