6 CHARLES T. BRUES. 



Such cannot be true of geographic poecilogony, but however the 

 origin and preservation of the several types of pcecilogenetic 

 development may be explained, the outstanding fact remains that 

 intraspecific poecilogony occurs. This is of interest in the present 

 connection as it shows that enormous changes in development 

 may readily appear in the early stages of an animal without 

 impressing themselves upon the later stages. , 



\Yhen applied to groups of insects rather than to single species, 

 Giard's views assume great interest from the standpoint of the 

 larval and pupal stages. If two groups of individuals of a single 

 species can reach the adult stage by separate paths, it is seen that 

 we have a much simpler case of apparently similar nature where 

 groups of species have developed highly adaptive methods of 

 development which are far from what might be expected if their 

 development had proceeded along the more conventional lines 

 of ancestral recapitulation. 



I shall not digress to attempt any discussion of the origin of 

 metamorphosis in insects nor of the way in which its increasing 

 complexity can be traced in living insects, from those showing 

 its primitive absence to others like the fly referred to above, in 

 which the larva is wholly unlike the imago not only in structure, 

 but in physiology and in its different ethological relationship 

 to a dissimilar environment. From the present standpoint, the 

 hypermetamorphosis of many insects is of especial interest and 

 I shall refer to this subject later. 



The properly trained zoologist is greatly outraged if he should 

 see a paper dealing with the larvae of certain insects "classified 

 as independent organisms," and will probably go no further to 

 inquire into the viewpoint of the writer. This is very natural 

 when we regard the whole animal and plant world as so closely 

 interdependent that a change in the abundance or distribution of 

 one species soon shows its effect upon a great number of others, 

 whose relations to the first species may not have been thought of 

 previously. Viewed in the light of pcecilogeny, or even after 

 one has worked for some time upon the classification of the 

 highly modified larv;e of some group of insects, it becomes far 

 from an absurdity and the more closely we inquire into the 

 matter the more clearly does it appear that many problems re- 



