^^"^ THE NEW EVOLUTION "^^""^ 



It might be supposed that the fact that the great majority of 

 these creatures are parasites indicates that they are simply 

 anomalous forms the peculiar characteristics of which have been 

 developed in accordance w^ith and as a response to their parasitic 

 habits. 



Parasitic habits, however, cannot produce structures which 

 are not already potentially present. Through parasitism certain 

 structural details may be profoundly altered, or a parasite may lose 

 various structural characters and through this loss become much 

 altered in its general appearance. This is well illustrated by the 

 various parasitic crustaceans and by the parasitic barnacles. But 

 no new structural complex is ever formed. 



Nature does not produce anomalies. To regard any creature 

 as anomalous is simply to confess our inability to understand it. 

 The living world is not chaotic — everything has its appointed 

 place in the general plan. 



The reason that the majority of these creatures are parasitic is 

 that their curious structure renders them incapable of competing 

 as free living forms with other types, while at the same time it 

 lends itself with peculiar facility to the specialized requirements 

 of a parasitic life. 



None of these creatures can be assumed to be descended from 

 the radially symmetrical coelenterates, or to have given rise to, or 

 to have been the ancestors of, any other forms of animal life. Yet 

 all forms of animal life must have been derived from the same 

 original ancestor or ancestral type. What, then, is their relation 

 to other animals? 



In their very earliest developmental stages — those immediately 

 following the division of the germ cell — they resemble all other 

 animal types. But they very soon diverge, both from the 

 developmental line leading to the radially symmetrical coelenter- 

 ates and from each other. Their later embryonic stages are 

 unique and very diverse. In some these recall in certain respects 

 the coelenterate planula, while in others they appear more like 

 the early embryos of some of the more complex animals. How 

 can this be reconciled with any developmental plan? 



The fundamental difference between the single-celled animals 

 or protozoans and all other animals is that the single cell of the 

 protozoan divides into two cells which separate completely from 

 each other, each half of the original cell becoming a separate 



[2-44] 



