CLASSIFICATION OF INSECTS. 13 



Portschinski (several papers), Osten Sacken ('87), Blanchard 

 ('93- '96), Banks ('12), MacGregor ('14), and Kodhain and 

 Bequaert ('16) have dealt with some of these larva' in a way 

 which is of interest in the present connection. As the specific 

 characters in these flies relate to so few structures, it is very 

 difficult to delimit the larger groups such as families, although 

 the species appear in great measure to have individual character- 

 istics of easy recognition. 



The classification of the several families of flies related to the 

 Muscidae has been the cause of much controversy among ento- 

 mologists and there is no question concerning the advisability 

 of utilizing the larvae in any attempt to elucidate their natural 

 affinities. Not excepting any animals, the species of some of these 

 families are distinguished by the most minute characters, so 

 slightly do the adults vary in structure. In very many cases, 

 it is already known that the larvae show more striking differences, 

 but it would be unwise at the present 'time to do more than to 

 predict that a comparison of adult and larval structure and of 

 habits and behavior in these insects, which appear to be under- 

 going a rapid evolution, will lead to results of great interest. 



Another group of insects in which it is possible to trace the 

 probable course of larval modification in the form of several 

 series is seen in the Trichoptera, Lepidoptera and Hymenoptera. 

 These orders appear to have been developed rather directly from 

 a group similar to the Panorpatae or Mecoptera which is repre- 

 sented, although not very extensively in the living fauna. In 

 these several orders the larva is primarily of the cruciform type, 

 but becomes apodous in some cases, more generally so in the 

 Hymenoptera, where only a small series of families retain the 

 caterpillar-like larva. 



Of all larval insects, the caterpillars of various butterflies and 

 moths are best known to the casual observer and they have long 

 attracted the attention of naturalists. In general form they are 

 remarkably uniform, with long cylindrical body, well developed 

 head capsule and trophi, functional thoracic legs and a series of 

 prolegs on certain segments of the abdomen differing greatly in 

 structure from the thoracic ones, but homologous with them. 

 In only a few Lepidoptera do the larvae become apodous or nearly 



