142 



ENTOMOLOGY 



Larva. Although larvae, generally speaking, differ from one another 

 much less than their imagines do, they are easily referable to their orders 

 and usually present specific differences. Larvae that display individual 

 adaptive characters of a positive kind (Lepidoptera, for example) are 

 easy to place, but larvae with negative adaptive characters (many Dip- 

 tera and Hymenoptera) are often hard to identify. 



Thysanuriform Larvae. Two types of larvae have been recognized 

 by Brauer, Packard and other authorities : thysanuriform and cruciform; 

 respectively generalized and specialized in their organization. The 

 former term is applied to many larvae and nymphs (Fig. 213, C) on 



FIG. 213. Types of larvae. A, B, Thysanura; C, thysanuriform nymph; E-I, cruci- 

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

 nata); E, Tenthredopsis (Hymenoptera); F, Lachnosterna (Coleoptera); G, Melanotus 

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



account of their resemblance to Thysanura, of which Campodea and 

 Lepisma are types. The resemblance lies chiefly in the flattened form, 

 long body, hard plates, long legs and antennae, caudal cerci, well- 

 developed mandibulate mouth parts, and active habits, with the accom- 

 panying 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 Blat- 

 tidae, Forficulidae, Perlidae and Ephemeridae, but occur also in the larvae 

 of some Neuroptera (Mantis pa) and Coleoptera (Carabidae and Meloi- 

 dae). These primitive characters are gradually overpowered, in the 

 course of larval evolution, by secondary, or adaptive features. 



