162 



ENTOMOLOGY 



Thysanuriform Larvae. Two types of larvae are recog- 

 nized by Brauer, Packard and other authorities : thysanuri- 

 form and cruciform; respectively generalized and specialized 

 in their organization. The former term is applied to many 

 larvae and nymphs (Fig. 210, C, D) on account of their resem- 

 blance to Thysanura, of which Campodea and Lepisma are 



FIG. 210. 



Types of larvae. /, B, Thysanura; C, D, thysanuriform nymphs; E-I, cruciform 

 larvae. A, Campodea; B, Lepisma; C, perlid nymph (Plecoptera) ; D, Libellula 

 (Odonata) ; E, Tenthredopsis (Hymenoptera) ; F, Lachnosterna (Coleoptera) ; G, 

 Melanotus (Coleoptera) ; H, Bombus (Hymenoptera) ; I, Hypoderma (Diptera). 



types. The resemblance lies chiefly in the flattened form, hard 

 plates, long legs and antennae, caudal cerci, well-developed man- 

 dibulate mouth parts, and active habits, with the accompanying 

 sensory specializations. These characteristics are permanent 

 in Thysanura, but only temporary in metamorphic insects, and 

 their occurrence in the latter forms may properly be taken to 

 indicate that these insects have been derived from ancestors 

 which were much like Thysanura. 



Thysanuriform characters are most pronounced in nymphs 

 of Blattidae, Forficulidae, Perlidae, Ephemeridae and Odonata, 

 but occur also in the larvae of some Neuroptera (Mantispa) 

 and Coleoptera (Carabidae and Meloidae). These primitive 

 characters are gradually overpowered, in the course of larval 

 evolution, by secondary, or adaptive, features. 



