204 THE PATH OF DEGENERATIVE EVOLUTION 



preserves one or other ; for instance, the leaves of 

 parasitic flowering plants continue to serve as 

 protectors of the buds, and degeneration does not 

 affect the part that has remained functional. It 

 is highly probable that the original function of 

 leaves was assimilative rather than protective, and 

 yet here it is the later function that is retained. 



Even when all function is lost, and the whole 

 structure degenerates, there is no reason why the 

 degeneration should retrace the evolution. In the 

 case of the atrophy of an organ in an individual 

 especially in such pathological instances as those 

 mentioned by Bibot, it may be that the latest 

 formed parts are the most fragile, and the most 

 ready to disappear ; but the path of atrophy is 

 quite different in the case of the gradual reduction 

 of an organ in a species. When an organ becomes 

 useless to a species, as in the case of the eyes of 

 deep-sea Crustacea, the only thing that matters to 

 the species is that it may be got rid of. Any 

 individual variation tending towards reduction will 

 be of advantage, and may be retained by natural 

 selection. There is no reason to suppose that such 

 individual variations appear in any inverse order ; 

 in fact we do not know that the appearance of 

 variations follows any law at all. Perhaps the 

 apparent inverse order of the degeneration of the 

 pineal eye in lizards may be explained from the 

 fact that the most recently acquired characters are 

 frequently the most variable. 



