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ENTOMOLOGY 
An anomalous beetle, Platypsyllus castoris, occurs through- 
out North America and also in Europe as a parasite of the 
beaver. 
The fleas, allied to Diptera but constituting a distinct order 
(Siphonaptera), are familiar parasites of chickens, cats, dogs 
and human beings. These‘insects (Fig. 30) are well adapted 
by their laterally compressed bodies for slipping about among 
hairs, and their saltatory powers and general elusiveness are 
well known. Their wings are reduced to mere rudiments, their 
eyes when present are minute and simple and their mouth 
parts are suctorial. 
Among Diptera, there are a few external parasites, the best 
known of which is the sheep tick (Welophagus ovinus), though 
several highly interesting but little-studied forms are parasitic 
upon birds and bats. 
The larvee of the bot flies (Céstridz) are common internal 
parasites of mammals. The sheep bot fly (Cstrus ovis) 
deposits her eggs or larve on the nostrils of sheep: the 
maggots develop in the frontal sinuses of the host, causing 
vertigo or even death, and when full grown escape through 
the nostrils and pupate in the soil. The horse bot fly (Gas- 
trophilus equi) glues its eggs to the hairs of horses, especially 
on the fore legs and shoulders, whence the larve are licked off 
and swallowed; once in the stomach, the bots fasten them- 
selves to its lining, by means of special hooks, and withstand 
almost all efforts to dislodge them; though when the bots have 
attained their growth they release their hold and pass with the 
excrement to the soil. Bots of the genus Hypoderma form 
tumors on cattle and other mammals, domesticated or wild. 
The ox-warble (H. lineata, Fig. 210, /) reaches the cesophagus 
of its host in the same manner as the horse bot, according to 
Curtice, but then makes its way into the subcutaneous tissue 
and causes the well-known tumors on the back of the animal; 
when full grown the bots squirm cut of these tumors and drop 
to the ground, leaving permanent holes in the hide. 
Parasitism in General.— Parasitic insects evidently do not 
