398 Introduction to Animal Morphology. 



the soft imago body speedily dries, and early dis- 

 charges the urine which had been accumulating during 

 the pupa-sleep. 



Some larvae have bristles, or, in Sphingidae, a 

 dorsal horn. The head bears a pair of procephalic 

 scales or lobes, in front of which is a proclypeus. The 

 larval antennse differ from those of the imago, and 

 joint with the front edge of the procephalic shield, 

 external to the articulation of the mandible, thus re- 

 sembling the antennas proper of Crustacea, while the 

 imago antennae, arising farther inwards and forwards, 

 are the homologues of the antennules [Zaddach). 

 Some larvae are dimorphic. 



CHAPTER XLVII. 



CLASS INSECTA. 



Insects are almost all terrestrial ; very few (Halo- 

 bates, Gyrinus) are marine. About 175,000 species 

 are known, which can be divided into two sub-classes, 

 according to the extent of their metamorphoses. 



Sub-class I. Ametabolica — with no, or imperfect 

 metamorphosis. 



This includes the following six Orders : — 



I. Mallophaga {Nitzsch) — wingless, flattened, ametabolic ; 

 parasitic on birds and mammals ; antennse 3-5 jointed ; eyes 

 simple ; mouth masticatory ; mandibles hook-like ; palps 

 four-jointed, or none ; meso- and metathorax mostly fused 

 abdomen 9-10 ringed, but with few (4-6) ganglia ; pharynx 

 muscular ; intestine simple. The antennae may be three- 

 (Trichodectes) or five-jointed, thread-like, with no maxillajy 



