40 



are now only a pair of black, horny mandibles. The segment immediately behind the 

 head, known as the prothoracic segment, bears a spiracle, or breathing orifice, and 

 others are situated in the anal, or posterior segment. 



When the larva is full grown its body contracts and changes in shape, becoming 

 what is known as a puparium. That is, the larva does not spin a cocoon in which to 

 pupate, but uses for this purpose its own skin, which becomes detached and hardened, 

 and within which the pupa forms and remains for from 5 to 7 days. This puparium is 

 of the shape of a grain of rice, from ^ to ^ of an inch long, and of a dark reddish-brown 

 colour. 



At the end of the time just mentioned the insect frees itself from the pupa-skin and 

 pushes its way out of its case, the anterior end of which splits off at the junction of the 

 thorax and abdomen, and falls back like the lid of a box. On emerging from his band- 

 box the fly, however, not yet ready to set out on his tour of visits and explorations ; his 

 ciothes do not fit him comfortably, nor is he yet the trim, natty little chap that we are 

 familiar with. His wings are soft, small and baggy, barely reaching to his waist, and 

 pressed against his sides. He is also pale, indeed nearly white, with perhaps a slightly 

 jaundiced appearance, due to his underground life and recent close confinement in a 

 dark cell. But he walks or runs rapidly about, respiring quickly and strongly, and in 

 an hour or so his wings expand and stiffen, the proper colours develope, and blithe and 

 agile he leaves his lowly birth-place in search of adventures. 



Before describing the fly in this final and perfect state, I will recapitulate its life- 

 history as already given. 



The eggs laid are about 120 in number, and in about twenty-four hours the larvae 

 are hatched. There are three stages of the larval state, and consequently two moults. 

 The first stage lasts about one day. The second stage lasts about one day. The third 

 stage lasts three or four days. The entire larval state lasts from five to seven days. The 

 pupal state lasts from five to seven days. The period from the time of hatching to the 

 exclusion of the fly lasts from ten to fourteen days in warm weather. — (Packard). 



We thus see that from the time the egg is deposited until the fly arrives at maturity 

 only about a fortnight elapses ; and when we consider that the fly, unlike many insects, 

 does not die immediately after depositing her eggs, but survives to perform that opera- 

 tion, perhaps, twice or thrice again, it will not be difficult to account for the rapid man- 

 ner in which the swarms increase toward the autumn. It was calculated by Keller that 

 if a fly deposited eighty eggs, and that only half of these produced females, she might in 

 one season be the progenitrix of upwards of two millions. Other authors have arrived at 

 a much larger number as the possible offspring in one season, but the smaller one will 

 suffice to show how rapidly they are capable of increasing. 



Although the common house-fly is so abundant, it so closely resembles allied species 

 that it is very difficult to distinguish it from some of them. The structural differences 

 by which entomologists recognize it are those of the mouth-parts, and venation of the 

 wings. 



The following is its description as taken from Packard : — 



" The body of M. domestica is black; the head has a longitudinal, reddish, oval, smooth 

 area on the vertex, with the orbits and adjacent regions golden (or silvery in some 

 lights) ; the hairs are black, and the antennae and plume are black ; the thorax is black, 

 tinged with golden grey on the sides, with three dorsal, grey, longitudinal bands, the 

 middle one most distinct, the two lateral ones partially interrupted in the middle and 

 continued on to the scutellum ; there is a broad, lateral, golden-grey band interrupted 

 by the sutures ; the base of the first abdominal segment has a yellowish band interrupted 

 in the middle ; on the middle of the end of the two succeeding segments is a triangular, 

 mesial, golden spot, with an oblique, irregular band on each side, and farther down the 

 sides golden ; terminal segments golden ; base of wings, scales, and halteres yellowish- 

 white ; legs black. The male differs from the female in the front between the eyes, 

 ^eing about one-third as wide as in the latter, while she is rather the smaller. Length, 

 •22 to -32 inch." 



This description, if borne in mind, will assuredly enable you without difficulty to 



