140 INSECTS. 



maggots make their appearance. The larvae of the 

 blow-fly are well known to the angler, who uses them 

 for bait, and calls them gentles. 



These larvae exhibit some interesting points of 

 structure. The jointed or ringed condition of the 

 body is distinct to the naked eye. The head is pro- 

 vided with two rudimentary palpi, placed each upon 

 a rounded papilla ; also with two brown curved and 

 horny hooks or jaws. On the posterior end of the 

 body are two brown spots, which consist of spiracles, 

 and have three sieve-like oblong orifices ; and at the 

 anterior margin of each segment of the body are very 

 numerous little short spines, with the points directed 

 backwards. These answer the purpose, to some extent, 

 of legs ; for when the larva is moving, and has forced 

 itself through the matter in which it burrows, the little 

 spines prevent the body being forced backwards as 

 the head is pushed forwards and meets any resist- 

 ance. 



To examine the structure of these larvse, the 

 gentles should be killed by immersion for a time in 

 warm water, and then dried by touching them with 

 blotting-paper. The hooks and palpi can be seen by 

 holding the body in the forceps as an opake object. 

 To observe the spiracles, the end of the body should be 

 cut off, and the animal matter washed away in a watch- 

 glass with water and a hair pencil, then spread out, 

 dried between two slides, and mounted in balsam. 



The larvae of the house-fly and of the blow- fly very 

 closely resemble each other, so much so that the 

 former are generally overlooked; hence it is often 

 wondered where flies come from, although they are 

 so numerous in every house. When the larvae of 

 these flies are fully developed, they gradually assume 

 a brown colour, the organs of the head are retracted, 

 and the skin becomes dry and hard. This is the 

 state of pupa, or chrysalis ; and while remaining in 

 this state of rest, the development of the wings, legs. 



