698 
ON A GAD-FLY GRUB. 
Department of the North, published, some years ago, a short Notice 
on the CEstrus Cuticolens of the horse, and has given a description 
of the larvce of this oestrus, of which we have, according to the 
text, made a full copy. 
At the present day, with Nature herself before our eyes, we 
feel satisfied that this description, confessed to be imperfect even 
by the author himself, viewed as a branch of natural history, is 
wanting in exactitude. And this induced him to introduce a 
portrait of the insect in question, with a fresh description of it 
more in accordance with the rigorous precision prescribed by 
science. 
Its character once well established, we shall be able readily to 
resolve the question, whether the oestrus in point be identical with 
the hypoderme of the ox, or whether it constitutes another species 
to be added to the genus hypoderma. 
The larva cuticolens (skin-habitant grub) of the horse has a 
cylindrical form, measuring more round in its fore than its hinder 
part. Tt is without brain or feet. Its body is constituted of eleven 
segments, including the one in which is found the buccal orifice 
(or mouth), which consists of a very small hole, edged with a 
black border* with some bristles around so fine as to be with diffi- 
culty perceptible by the naked eye. The foremost segment is of 
all the smallest. From this the segments, as far back as the fifth, 
grow gradually larger ; while, on the contrary, the five posterior 
continue to diminish as they approach the hinder part. These 
segments, examined upon their ventral surface, with the exception 
of the two last, are divided transversely by slight grooves into two 
unequal halves, each furnished with a great number of spinous tu- 
bercles, whose points, upon the anterior half of the segment, are 
directed backwards, but forwards upon the posterior half. Two 
cribriform plates, the sole organs of respiration with which the grub 
is provided, are seated upon a sort of flattened termination of the 
anal segment. 
Alike in this respect to the hypoderma hovis, the skin-habitant 
grub of the horse has, contrary to what is observed in the majority 
of cases, the inferior surface of the body convex, while the dorsal 
side of the segments is slightly concave. Such form is in this 
manner perfectly fitted to the spherical cavity which serves as 
a habitation for the parasite. It is worthy of remark, that the 
dorsal surface of the body is without bristles, save upon the two 
or three foremost segments. The general colour of the skin is 
white ; the bristly tubercles alone being brown, more or less 
shaded. The skin itself is translucid and vesiculous, as it were. 
In size the larva is much below the hypoderma hovis, since it does 
