CHAPTER VI 

 THE STRUCTURE OF THE HOUSE-FLY 



The house-fly has quite the typical insect form, inas- 

 much as there are three well defined sections of body 

 the head, the chest or thorax, and the abdomen ; 

 also it has three pairs of legs, each with nine joints, of 

 which five joints constitute what may be called the 

 foot. The twelve segments of the maggot are observ- 

 able as twelve rings in the puparium, but in the fly the 

 three which form the thorax look like one, whilst the 

 eight which should theoretically exist in the abdomen 

 look like four or five, until the rings of the ovipositor 

 are counted. 



The illustration on page 39 will make plain how 

 the permanence of the twelve-segment structure (con- 

 spicuous in the larval stage) has been thought to persist 

 throughout the life-cycle, but at the same time will 

 disclose how great is the change in the relative 

 proportions of these segments. 



The prominent features of the hemispherical head 

 are the two large compound eyes and the proboscis or 

 trunk-like mouth. The antennae or horns are very short 

 appendages with three joints ; small plume-like 

 projections, called arista, are attached to the third 

 segment ; the horns hang down over a hollow in the 

 middle of the face, and are insignificant in size when 



