ON A GAD-FLY GRUB. 
697 
tion — first, in the essential identity of the structural elements ; 
and, secondly, in its benignant character ; — rather than create 
new pathological distinctions (always inconvenient and unprofit- 
able, unless established upon very weighty reasons), I regard the 
tumour as an ossifying enchondroma : though, in the present state 
of knowledge, it must be considered a very rare, if not isolated, 
example.” 
Foreign Extracts. 
On a Gad-fly Grub found underneath the Skin 
of the Horse. 
By M. N. JOLY, Professor of Zoology to the Faculty of Science. 
[Read at the Agricultural Society of the Haute-Garonne, April 1849.] 
We know that the horse harbours several species of cestrides 
(or gad-flies) in his body, of which those best known are the oestrus 
equi } the oestrus veterinus , and the oestrus hcemorrhoidalis , whose 
habitations are the stomach and intestines. But what we do not 
seem to be generally aware of, is, that under the skin even, larvce 
(or grubs) of the diptera family breed and give rise to the forma- 
tion of tumours analogous to such as strike our notice, at certain 
times of the year, upon the bodies of our large ruminants ; and 
particularly of those who appear, in all other respects, to enjoy the 
best health. Redi and Huzard (the father) have spoken of these 
inhabitants of the skin of the horse. Bracy Clark, likewise, has 
mentioned them in his “ Essay on Bots;” but he regards them as 
identical with those of the hypoderma species which exist under- 
neath the thick skin of the ox. 
Dr. Roulin, of the Institute, in his Researches on certain 
Changes observed in Domestic Animals transported from the Old 
to the New Continent , expresses himself as follows : — In the hatos 
of Llanos , the horses are almost entirely left to themselves. They 
are driven up only from time to time to keep them from becoming 
quite wild, to take off them the larvce of the cestri, and to mark 
the foals with a red hot iron. To what species do these American 
larvce belong 1 As yet we remain in ignorance of this. 
Last of all, M. Loiset, a celebrated veterinary surgeon of the 
