STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 35 



Secondary Larva. — ^Larvae like the adult, and with a few provisional larval organs 

 — Ephemerida, Plecoptera, Cicadidcc, Odonata, Coccidce. 



Tertiary Larva. — Larvae unlike the adult and with numerous provisional larval 

 organs — Lcpidoptera, Dlptera, Coleoptera, Hymcnoplera, etc. 

 ■ Classificalion of Tertiary Larva. 

 A. Larvffi without prolegs. 



B. Larvae with well-formed sternum. 



C. Larvae more or less strongly chitinized; thorax or at least the 

 prothorax differing from the other segments quite noticeably, 

 large or more strongly chitinized, or otherwise sculptured; head 

 generally with lateral eye points. Examples: Rhaphidians 

 Ant-lions, Carabida, Dytiscida, Silphida, Coccinellida, Elalerida, 

 Chrysomelida. 

 CC. Larvae weakly chitinized, soft skinned, and mostly whitish, 

 but with chitinized dark head; thorax differing but little from 

 the other segments. Examples: White Grubs, Stag Beetles, 

 Dung Beetles. 

 BB. Larvae with poorly developed or rudimentary sternum. Examples: 

 Many Cerambycids, Sirex. 

 BBB. Larvae with sternum whoUy atrophied or undeveloped. 



C. Larvae with a head-capsule and typically formed mouth-parts. 

 Examples: Bark Beetles, Snout Beetles, Bees, Wasps, Ants, 

 Ichneumons, Midges. 

 CC. Larvae without a head-capsule or well-formed mouth-parts. 

 Examples: Most Diptera. 

 AA. Larvae with prolegs. 



B. Larvae usually with five pairs of prolegs. Butterflies and Moths. 

 BB. Larvae with more than five pairs of prolegs. Sawflies. 



Provisional Larval Organs. — Provisional larval organs are those 

 which belong to the larva and not to the imago. According to Escher- 

 ich such organs represent adaptations for special functions, so that the 

 more numerous these organs are the greater the difference in mode of life 

 and in appearance between the larva and imago. As the imago is 

 older phylogenetically than the larva the larval organs have arisen in 

 a secondary manner. 



"Secondary" larvae possess numerous imaginal characters, so that 

 the form of the imago remains more or less evident. In "tertiary" 

 larval forms the characters of the imago are so repressed by those of the 

 larva that a new form unlike the imago results. 



Larval organization distinct from that of the imago may be observed: 

 (i) in the amount of chitinization, the color and the armature of hairs, 

 bristles, spines of the skin; (2) in the number of glands; (3) in the form 



