Vol. XXXVII. July, IQIQ. No. I. 



BIOLOGICAL BULLETIN 



THE CLASSIFICATION OF INSECTS ON THE CHAR- 

 ACTERS OF THE LARVA AND PUPA. 1 



CHARLES T. BRUES. 



Knowledge of the preparatory stages of insects is still very 

 fragmentary in comparison with the much more extensive 

 information available concerning the comparative structure and 

 classification of the imaginal forms. These developmental 

 stages are of great interest, however, and have been neglected 

 only for practical reasons incident to the vast extent of insects 

 as a group, and the impossibility of correlating the adult and 

 preparatory stages without the laborious process of breeding 

 each individual species. 



A comparative study of insect larvae and pupae throws much 

 light on the origin and development of metamorphosis, a con- 

 dition which reaches its climax in the highly specialized insect. 

 It is also essential to an understanding of the varied adaptations 

 of insects, many of which appear in such a form that their 

 biological significance cannot otherwise be recognized. The 

 independent adaptations of insect larvae are peculiar phenomena, 

 which must aid greatly in the application of the biogenetic law 

 to insects; in fact any attempt to correlate insect ontogeny with 

 phylogeny must be undertaken with careful attention to the 

 characteristics of larval development. Such functional and 

 structural modifications in larval insects, have I think, not 

 received the attention which they deserve. They have usually 

 been considered as phenomena without close counterpart among 

 other animals, or at least as such an exaggerated expression of 

 metamorphic development that they could not readily be re- 



1 Contributions from the Entomological Laboratory of the Bussey Institution, 

 Harvard L T niversity, No. 157. 



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