24 ENTOMOLOGY 



metamorphosis, which appears in Neuroptera and attains its 

 maximum development in Diptera and Hymenoptera. 



With Neuroptera the cruciform type of larva appears, as a 

 derivative of the earlier thysanuriform type. The larva of 

 Mantispa, as Packard has shown, actually passes, during its 

 individual development, from the primary, thysanuriform 

 stage to the secondary, cruciform condition. 



Mecoptera form an isolated order, though their caterpillar- 

 like larvae, with eleven or twelve pairs of legs, suggest affini- 

 ties with Lepidoptera and, more remotely, with the tenthred- 

 inid Hymenoptera. 



Trichoptera, while much like Mecoptera in structure and 

 metamorphosis, are undoubtedly closely related to Lepidop- 

 tera; in view of the extensive and deep-seated resemblances 

 between caddis flies and the most generalized moths (Microp- 

 terygidae) there is little doubt that Trichoptera and Lepi- 

 doptera originated from the same stock. 



The origin of the coherent group Coleoptera is by no means 

 clear, although thysanuriform larvae occur frequently in this 

 order. Packard suggests that both beetles and earwigs arose 

 from some thysanuroid form or that the primitive coleopterous 

 larva sprang from some metabolous neuropteroid form. In 

 any linear arrangement of the orders the position of Coleop- 

 tera is largely arbitrary, and here the order is intruded between 

 Lepidoptera and Diptera simply for want of a more satisfac- 

 tory place. 



Lepidoptera, Trichoptera and Mecoptera are probably 

 branches from one stem. Lepidoptera, Diptera and Hymen- 

 optera are regarded by Packard as having had a common 

 origin from metabolic Neuroptera. 



Among Diptera, such larvae as those of Culicidae are com- 

 paratively primitive, according to Packard, and larvae of Mus- 

 cidae are secondary, or adaptive, forms. 



Siphonaptera used to be regarded as Diptera and are prob- 

 ably an offshoot from the dipteran stem. 



The most primitive hymenopterous larvae are those of the 



