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order}. The most have no proper head, but a very moveable mouth 
well adapted for extension, and two horny hooks curved downwards. 
The skin of the larva when it changes to a pupa is not cast, but 
becomes hard, and is changed into the covering of the pupa; the 
anterior extremity becomes thicker and rounder, and the whole 
recalls the form of an oval keg. The perfect insect, by moving its 
head, which is extended forward like a bladder, breaks this shell at 
its upper extremity, whilst a piece of it springs open like a lid. 
Few genera of this family are in the perfect state carnivorous, 
most of them living on flowers and plants. 
Phalanx I. Proboscis in some very short, in others none, in 
place of proboscis and palps three tubercles ((@strus L.) 
Larve parasitic, some living beneath the skin, others in the 
frontal sinuses, or in the intestinal canal of mammalia. 
@) Proboscis small. 
Genera: Cephenemyia Larr., Cuterebra Cuarx, Latr., T'rypo- 
derma WIEDEMANN. 
b) Proboscis none. 
Genera: Hypoderma CuarK, (strus Mxic.), Hdemagena CuarKk, 
Cephalemyia CuarK, Colax WiEpEM., Wstrus CuarK, (fastrus 
MEIG.) 
Note.—Antenne triarticulate, with seta naked in most, in Cute- 
rebra plumose. Gastrus Meta. differs from Wstrus Mrtc. by the 
naked poisers, and wings without a transverse nervure at the apex. 
Comp. CuarK, Observ. on the genus Estrus, Trans. of the Linn. Soc. 11. 
1796, p. 289, &c.; the same, An Essay on the Bots of Horses, &c., London, 
1815, 4to, with fig.; the same, On the Insects called Oistros by the Ancients, 
Trans. Linn. Soc. XIX. 2. 1843, pp. 81—94. 
A. Numan Waarnemingen omtrent de horzelmaskers, welke in de maag 
van het paard huisvesten, Amsterdam, 1834, 4to, mit pl. 
J. L. C. ScHR@DER VAN DER Koux, Mémoire sur V Anatomie et la Physiol. 
du Gastrus equi, Amsterdam, 1845, ay. pl. 
Sp. GBstrus equi Fasr., Gastrus equi Metc., Guin, Iconogr., Ins. Pl. ror, 
fig. 5, CLARK, Essay on the Bots, Pl. 1. figs. 13, 14, (LInNmUS described 
this species under the name of @strus Bovis). About 5 lines long, body 
1 In these Boucnsé has frequently observed a moulting ; Beitrdge zur Insektenkunde, 
in Nov. Act. Acad. Ces. L. Car. Tom. xvil. 1. 1835, p. 498. 
