42 ENTOMOLOGY FOR MEDICAL OFFICERS 



with a head so small as to be almost invisible, and without 

 appendages except a pair of minute papilliform antennae 

 and a pair of chitinous mouth-hooks. Some grub-like larvae 

 may have, in addition, stumpy pseudopods like those of 

 caterpillars, on some of the segments. 



Another type of larva is exemplified by that of the 

 mosquito, which has a distinct head, thorax, and abdomen, 

 the head being provided with eyes and well-pronounced 

 antennae, and also with mandibles, maxillae, and other organs 

 for discriminate feeding. 



Dipterous larvae are sometimes classified according to the 

 arrangement of their spiracles or breathing-openings. Those 

 that have two pairs of spiracles — one pair at each end of 

 the body — are known as amphipneusttc (a^i^/= at both 

 ends, and TrvevaTiKa = things for breathing) : those that have 

 only one pair of spiracles placed at the posterior end of the body 

 are called metapneustic dmerd = behind, and irvevcrTiKa) ; while 

 peripneustic larvae (7re/)/ = round about, and Trveva-TiKa) are 

 those with numerous spiracles arranged in segmental pairs 

 along either side of the body. 



The larvae of Diptera show much diversity in mode of 

 life. Some live in water, both fresh and salt, and are 

 thoroughly aquatic animals ; many live in decaying organic 

 matter of all kinds ; others are parasites of living plants ; 

 others are parasites of the larvae of other kinds of insects ; 

 others are intestinal and subcutaneous parasites of vertebrate 

 animals; others are predatory and rapacious, seizing other 

 insects and small animals and eating or sucking them ; while 

 there is one, known as the Congo floor-maggot, which is a 

 blood-sucker and has much the habits of a bed-bug. 



The. pupa may be either "coarctate" (Lat. coarctatus = 

 confined, i.e., confined in its larval skin), or "obtected" 

 (Lat. obtectus = ^\o\.^cX.&A, i.e., merely protected by a chitinous 

 secretion). 



In the coarctate form the pupating larva shrinks in its 

 skin, so that the resulting pupa lies in a case or puparium, 

 formed by the hardened skin of the larva. 



In the obtected form the larva as it pupates casts off its 

 skin, and the pupa is enveloped only in its own chitinous 

 pellicle. 



