DIPTERA, 357 
(Estrus, Lin., 
Which is very distinct, as in place of the mouth we find but three 
tubercles, or slight rudiments of the proboscis and palpi. 
These Insects resemble large and densely pilose flies, and their hairs 
are frequently coloured in bands like those of the Bombi. Their an- 
tenn are very short; each one is inserted in a fossula over the front, 
and terminated by a rounded palette with a simple seta on the back, 
near its origin. Their wings are usually remote; the alule are large 
and conceal the halteres. The tarsi are terminated by two hooks 
and two pellets. 
These Insects are rarely found in their perfect state, the time of 
their appearance and the localities they inhabit being very limited. 
As they deposit their eggs on the body of various herbivorous quadru- 
peds, it is in woods and pastures that we must look for them. Each 
species of (Estrus is usually a parasite of one same species of some 
mammiferous animal, and selects for the location of its eggs the only 
part of its body that is suitable for its larvee, whether they are to re- 
main there, or pass from thence to the spot suited for development. 
The Ox, Horse, Ass, Rein-deer, Stag, Antelope, Camel, Sheep and 
Hare are the only quadrupeds yet known, which are subject to be 
inhabited by the larvee of the CHstri. They seem to have an extraor- 
dinary dread of the Insect when it is buzzing about them for the pur- 
pose of depositing its eggs. 
The domicil of the larve is of three kinds; we may distinguish 
them by the names of cutaneous, cervical, and gastric, as some live 
in the lumps or tumours formed on the skin, others in some part of 
the interior of the head, and the rest in the stomach of the animal 
destined tosuppert them. The eggs that produce the first are deposited 
by the mother under the skin, by means of a squamous ovipositor com- 
posed of four tubes fitting one within the other, armed at the end 
with three hooks and two other appendages. This instrument is 
formed by the last annuli of the abdomen. These larve, called taons 
by the farmers,are not compelled to change their domicil, finding 
themselves, when hatched, in the midst of the purulent matter 
on which they feed. The ova of the others are simply deposited and 
glued to various parts of the skin, either in the vicinity or the natural 
cavities into which the larve are to penetrate and take up their abode, 
or on those spots which the animal is in the habit of licking, in order 
that the larvee may be transported on its tongue into its mouth, where 
they can proceed to their destined dwelling. Thus, the female strus 
ovis places her eggs on the internal margin of the nostrils of the Sheep, 
which is no sooner aware of it, than it becomes agitated, strikes the 
earth with its feet, and flies with its head to the ground. The larve 
insinuates itself into the maxilliary and frontal sinuses, and clings to 
their lining membrane by means of the two stout hooks with which 
its mouth is armed. It is thus also that the Gstrus equi deposits 
her eggs at intervals, without alighting, and by balancing her body 
in the air, on the inner side of the legs of the Horse, on the side of 
the shoulders, and rarely on the withers. The C. hemorrhoidalks, 
whose larvee also inhabit the stomach of the same animal, places her 
