PHYLUM ARTHROPODA 



243 



FIG. 134. Beetle (Crioceris) 

 with larva. (After Guerin 

 and Percheron.) 



microscopic scales to which the various colours of the wing 

 are due. In the Beetles (Fig. 134), Locusts, and others, on 

 the other hand, the posterior wings 

 alone are membranous, the anterior 

 pair being converted into hard 

 and tough cases the elytra which, 

 when folded up, cover over and pro- 

 tect the delicate posterior wings. 

 In the Hemiptera the anterior wings 

 are thick and opaque at the bases 

 only. In the Diptera (Fig. 135), 

 the anterior wings alone are de- 

 veloped, the posterior being repre- 

 sented by vestiges, the halteres or 

 balancers. In the Bee parasites 

 (Strepsiptera) the posterior pair of 

 wings are alone developed. In 

 some Insects (Springtails, Lice, 



Fleas) wings are entirely absent in all stages. In others, 

 again, they are present in one sex usually the male and 

 absent in the other. 



The abdomen is devoid of any paired limbs in the adult 

 except at the posterior extremity, where there are frequently 

 appendages in the form of stings, ovipositors and genital 

 processes, some of which may be of the nature of modified 

 limbs. 



The enteric canal (Fig. 136) consists of a number of parts. 

 It is nearly always considerably longer than the body, and is 

 relatively longer in vegetable-feeding than in carnivorous 

 forms. The mouth le"ads into a buccal cavity into which 

 the ducts of a pair of large salivary glands open, and which 

 communicates with a narrow oesophagus (as.) dilating 

 behind into a crop (cr.} for the storage of food. The place 



R 2 



