II] LARVA 21 



The larvae are generally of the form known as maggots. 

 They are without exception destitute of true thoracic legs, 

 although in some groups stumpy pseudopods, resembling those 

 of the caterpillar, may be present. These pseudopods vary 

 greatly in their arrangement ; sometimes they are provided 

 with recurved hairs. 



The larvae may be divided into two groups according to 

 the size of the head. In the cruciform maggots the head is 

 so small as to be almost invisible and these are termed acepha- 

 lous larvae (e.g. Glossina). In the eucephalous larvae there is 

 a well-marked head provided with mandibles, and usually 

 there is a distinct thorax and abdomen (e.g. Anopheles). 



The tracheal system exhibits great variety and the larvae 

 may be classified according to the arrangement of their spiracles. 

 In the peripneustic forms, the spiracles are arranged along the 

 sides of the body, one pair to each segment ; in the amphi- 

 pneustic forms there are two pairs of spiracles, one at each end 

 of the body ; whilst in the metapneustic forms there is only one 

 pair of spiracles placed at the posterior extremity of the body. 

 The great majority of aquatic larvae belong to the latter 

 type and there are often very elaborate devices for keeping 

 the tip of the body in communication with the atmosphere 

 so that air can enter the spiracles. 



The habitat of the larvae is much more variable than their 

 structure, and they display great diversity in their mode of 

 life. The majority of the maggot-like forms live in decaying 

 organic matter, whilst nearly all the eucephalous larvae are 

 aquatic, occurring in both fresh- and salt-water and feeding 

 either on vegetable matter, or preying on other small animals. 

 A certain number of them are parasites, occurring in both plants 

 and animals, and there is one form, the Congo floor-maggot, 

 which sucks the blood of human beings and in its method of 

 feeding somewhat resembles the bed-bug. 



The pupa may be either oblectate or coarctate. In the former 

 case the pupa is merely protected by a thin chitinous pellicle 

 and the outlines of the various appendages of the future insect 

 can be clearly distinguished through this covering as, for 

 example, in the mosquito. In these obtectate forms the 



