93 
DIPTERA. 
Syn. Diopsis Indica, Westw. in Trans. Soc. Linn. vol. 17, p. 299. 
Diopsis Ichneumonea, Donovan , Is# edit. 
The appearance of this curious insect is peculiarly striking. Nothing can be more 
singular than the disposition of the eyes, which are situated at the extremity of two 
long immoveable pedicles arising from the head, most exactly in that part which in 
other insects hears the antennae. In this particular the Diopsis differs not only from 
other insects of the kindred genera, but also from all the other kinds we are acquainted 
with. Some few of the Cancri, &c. have indeed the eyes placed at the extremity of 
elongated pedicles, as is, for example, instanced in the Cancer angulatus, yet these are 
obviously dissimilar in construction, for they are moveable at the base, and may be 
directed towards any object, at the will of the animal, with the utmost facility; but to 
accomplish this, the motion of the pedicle in the Diopsis must be necessarily accom- 
panied by that of the head, or even of the whole body. The eyes of the latter are 
notwithstanding so conveniently stationed at the globular extremity of the pedicles, 
as to embrace a far more comprehensive range of sight than is usual with the generality 
of insects. 
To the inexperienced entomologist, the Diopsis would rather seem to be fur- 
nished with remarkable horns, and to be destitute of eyes, although the latter are so 
very conspicuous when they are pointed out; it is, on the contrary, the true horns, or 
antennae, that are so minute as to be most likely to escape attention, for each of 
these consists only of a single setaceous hair, or bristle, seated on a very small tubercle 
just beneath the eye. 
It has been previously intimated, in the observations on the genus Paussus, that 
the first account of the Diopsis was inserted in a small tract published by Linnaeus, at 
Upsal, in 1775. From this we learn, that both the Diopsis and the Paussus were 
found by Andreas Dahl, among a parcel of insects in the possession of Dr. Fothergill, 
of London, by whom they were sent to Linnaeus. These consisted chiefly of insects 
collected in North America and Guinea, but the habitat, either of the Paussus, or the 
Diopsis in particular, it is very certain was by no means exactly known. Fuessly 
notwithstanding describes the D. ichneumonea, upon this ambiguous authority only, as 
a native of Cayenne, and after him Gmelin notes the same insect from South America, 
and Guinea, perhaps with as little reason. Latreille tells us it is from the coast of 
Angola, on the information of Perrin, a zealous naturalist of Bordeaux. Donovan’s 
specimens of the insects here figured, and which he says are most assuredly the 
Diopsis ichneumonea of Linnaeus, were brought from Bengal, where they were dis- 
