THE BOT OF THE HORSE. 
157 
not sufficient to establish the proper character of the species. 
The fact 5 however, is accidental and insignificant. Whether 
found isolated, or in small or large groups, we shall always 
discover small, large, red even to intensity, and pale larvae. 
I do not know how it happens that, in a herd of colts, there 
are individuals in whom larvae infest the oesophagus, not be- 
yond the oesophagus, up to the time they attain about half of 
their growth; while in others they do not stop here, but pro- 
ceed straight to the stomach, and remain herein up to the eve 
of their first metamorphosis, when they make their exit to fix 
into the posterior part of the rectum, from which they become 
detached, according as their development gets completed. 
Some larvae are always smaller than others, and are often 
found isolated beyond the pylorus, though still cannot be 
viewed as a particular species ; which is owing partly to migra- 
tion, and partly to the death of the horse, whose circulation 
has ceased, and with it the temperature of the body. Under 
such circumstances, the stronger larvae detach themselves 
instinctively, to go in search of aliment and heat. In general, 
these larvae are found the more scattered about on the intes- 
tine according as the death of the animal takes place nearer 
to the month of August. 
These observations being premised, I shall give the de- 
scription of such species of bots as are mentioned by the best 
authors, in order to afford my readers an opportunity of judging 
if 1 be correct in admitting but a single species of horse-bot, 
different, be it understood, from that described by Yallisnieri, 
who believes it to breed within the intestines of the ox, and 
that on occasions it has proved the cause of the bovine pest 
which raged in his time ; different also from another described 
by Linnaeus, which is in the hypodermis of the ox. The cha- 
racters of these oestrides being given, I shall extend my 
observations to their manner and habits, speak of the events 
I have observed through the presence of their larvae in the 
gastric cavity, especially of colts, and place at the conclusion 
of my investigation the means I have made use of for the 
expulsion of them from the bodies of animals, — an object of 
the greatest interest in practice, and that to which our 
Journal is principally directed. 
1. — HORSE BOT. 
(GEstrus Equi, Clark; (Eslrus Bovis , Linn.; Gastrus Equi , 
Meigen.) 
This species is common in the south of Europe and in the 
East. The female deposits her eggs on the hair of the tibial 
xxvii. 21 
