364 
OESTRUS, 
reddish colour, except the points, which are black. 
These larvae evidently receive their food at the 
small end, by a longitudinal aperture, which is si- 
tuated between two hooks or tentacula. Their 
food is probably the chyle, which, being nearly 
pure aliment, may go wholly to the composition 
of their bodies without any excrementitious re- 
sidue, though on dissection the intestine is found 
to contain a yellow or greenish matter, which is 
derived from the colour of the food, and shews 
that the chyle, as they receive it, is not perfectlj'^ 
pure.” 
‘‘ They attain their full growth about the latter 
end of May, and are coming from the horse from 
this time to the latter end of June, or sometimes 
later. On dropping to the ground they find out 
some convenient retreat, and change to the chry- 
salis i and in about six or seven weeks the fly ap- 
pears.” 
To the above account by Mr. Clark I have only 
to add that the most successful method of obtain- 
ing the flies from the chrysalis is by, taking the 
larvie, when fresh dropped from the horse, and 
immediately enclosing them separately in balls of 
fresh horse-dung, wdiich must be kept in a w^arm 
situation, and sprinkled every second or third day 
with w^ater: the animals will thus be preserved in 
a proper degree of warmth and moisture, and the 
flies w ill make their appearance in the usual time. 
Oestrus Ovis, or the Sheep Gad-Fly, is so named 
from its larva inhabiting the nostrils and frontal 
.sinuses of Sheep in particular, though it is also 
