54 THE INSECT WORLD. 



of their tails being on the surface of the water. He then increased 

 the depth of the water by degrees ; and, as it got deeper, observed 

 that tlie tail of each worm became longer. These tails, which at 

 first were only two inches long, at last attained to five. 



It will be remarked that the body of each worm does not exceed 

 five lines in length. The tail is a peculiar organ, by the aid of 

 which the worm breathes, although its body may be covered by 

 water to the depth of several inches. It is composed of two tubes, 

 one of which shuts into the other, like a telescope. Re'aumur calls 

 it the breathing tube. It terminates in a little brown knob, in 

 wliich, according to Reaumur, are two holes for the purpose of 

 receiving the air, and which have five little tufts of hair, which float 

 on the surface of the water. When the time comes for the meta- 

 morphosis of these worms, they come out of the water and bury 

 themselves in the earth ; the skin then hardens and becomes a sort 

 of cocoon. In this cocoon the insect loses the form of a worm, and 

 takes by degrees that of the pupa, which it keeps until circumstances 

 cause it to throw off its last coverings, and to appear in the winged 

 state. 



What an eventful life ! what a life full of changes and turns of 

 fortune is that of these insects, which pass the first and longest 

 period of their existence under water, another part of their life under 

 the ground, and, finally, after having existed in these two elements, 

 enjoy, high in the air, the pleasures of flight ! 



The third group of Brachycera is that of the Dichceta ; that is, 

 those flies having two-fibred suckers. Among these are classed the 

 CEstri, the Conopes, and the flies properly so called. 



The genus CEstnis, the Gad, Bot-fly, or Breeze, comprises those 

 formidable insects which attack the horse, the sheep, and the ox.* 

 The labours of Re'aumur, in his admirable Memoirs, and those of 

 M. Joly, Professor of Zoology to the Faculte des Sciences de 

 Toulouse, who published some most valuable researches on this 

 subject, in 1846, will guide us in the following brief explanation. 



The following is the description given by M. Joly of the Gad-fly 

 (CEstrus eqni) represented in Figs. 41, 42, which are taken from a 

 drawing which accompanies that naturalist's Memoirs. 



The head of this insect is large and obtuse ; the face light yellow, 

 with whitish silky fur ; the eyes blackish ; the antennae ferruginous ; 



* Mr. Bates, in his interesting "Naturalist on the Amazons," mentions an 

 CEstriis as occurring in those regions, which deposits its eggs in the human flesh, 

 the larva causing a swelling w^hich resembles a boil.— Ed. 



