(ESTRID^. 403 



shut by the protruding suctorial flaps. The wings do not have 

 the auxiliary vein running towards the anterior margin ; the an- 

 terior basal cell is very short ; and the discoidal cell coalescent 

 with the second basal cell, while the posterior basal cell is very 

 small. They are mostly "found on the leaves of aquatic plants, 

 on stones partly overflown with water, on dams and near water- 

 falls ; some of them are able to run rapidly over the water, even 

 when it is rippled by the wind {Hydoplioriis) ; others are fond 

 of salt or brackish waters {ApJirosyhcs, Thinophilus and some 

 Hydropliorus) ; the species of Medetems prefer dry situations, 

 and are found on stumps of trees, fences, etc., even in very 

 dry and hot weather." 



QSsTRiDuE Leach. Bot-flies, Breeze-flies. In these flies, so 

 interesting in their habits, the body is stout, hairy, like the 

 Humble bees, and they are easily recognized by having the 

 opening of the mouth very small, with rudimentary oral or- 

 gans. The middle part of the face is exceedingly narrow, and 

 the minute antennae are inserted in rounded pits. The eggs 

 hatch very soon after laying, and Riley (First Annual Report 

 on the Noxious Insects of Missouri, p. 164) thinks, from the 

 testimony of three independent witnesses, that the sheep bot- 

 fly is viviparous, the larvae hatching within the body of the 

 parent, who deposits in the nostrils of the sheep the "perfectly 

 formed and living grub." 



The larvae are, in general, thick, fleshj^, footless grubs, con- 

 sisting of eleven segments exclusive of the head, which are 

 spined and tuberculated, the former in rows, which enable them 

 to move about readily when living under the skin or in the 

 frontal sinus and thus greatly irritate the animals on which they 

 live. The stigmata are placed in a scaly plate on the thick- 

 ened posterior end of the body. The mouth of the cutaneous 

 larvae consists simply of fleshy tubercles, while in those species 

 that live in the stomach and frontal sinuses of their hosts, it is 

 provided with horny hooks. While in this state they moult 

 twice, and then attain their full size. They feed on the puru- 

 lent matter originating from the irritation produced by the 

 movements of their bodies. Just before assuming the pupa 

 state, the larva leaves its peculiar habitat, descends into the 



