“PARASITES OF ANIMALS. 19 
egos. There are numerous genera and species, each of which 
lives, in the larval state, upon some particular species of 
mammalia, and usually in some particular part of the ani- 
mal. In the tropical parts of America there are species which 
live beneath the human skin, in tumors that they cause. The 
larve are usually thick, fleshy grubs, destitute of fect, but 
generally provided with rows of hooks or spines; by means of 
which they move about in their burrows. The breathing 
pores are in one or two scaly plates at the thick posterior end 
of the body. In those that are parasitic in the stomach, the 
mouth has horny hooks by means of which they cling to the 
lining membrane ; but in those that live in tumors under the 
‘skin, there are no hooks to the mouth, but only fleshy 
tubercles. They live on the matter, or pus, which is caused 
by the irritation that they produce. : 
The flies generally have a stout, hairy body, sometimes 
looking somewhat like humble-bees. The female has a more 
pointed abdomen, with an extensible ovipositor. The an- 
tenne are very small, and placed in little pits. The mouth 
organs are almost abortive, and the mouth very small, for 
these flies take little or no food in their winged state, this 
period of their lives being wholly devoted to the reproduction 
of their kind. The species that infest cattle, sheep, and 
horses have been transported to nearly all parts of the world 
where these animals are reared; but there are many native 
species that are found only in the wild animals. * 
The Bot-fly of Cattle (Hypoderma bovis Latr). Figures 22, 23. 
This fly is densely covered with hairs, except upon the 
thorax, which is partially naked and black, broadly banded 
with white and yellow. The abdomen is banded alternately 
with yellowish white and black, and with reddish orange at 
the end. The front of the head is dirty ashen, with yellowish 
white hairs. They appear from June to September, and the 
females lay their eggs on the backs of cattle. According to 
* One species, Cuterebra emasculator, described by Fitch, lives in the scrotum of 
squirrels, and destroys one or both testicles. In some parts of the country it is 
often quite common, and doubtless greatly diminishes the number of squirrels. 
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