DIPTERA. 461 



antennae on its Bides, and the other constituting the apparatus of manducation. 

 The inferior and oral cavity of the head is occupied by a membrane ; from its 

 extremity issues a sucker arising from a little bulb or projecting pedicle, com- 

 posed of two closely approximated threads or seise, and covered by two 

 coriaceous, narrow, elongated, and pilose laminae which form its sheath. 



The body is short, tolerably broad, flattened and defended by a solid skin 

 almost of the consistence of leather. The head is more intimately united to 

 the thorax than in the preceding families. The antennae, always situated at 

 the lateral and anterior extremities of the head, sometimes form a tubercle 

 bearing three setae, and sometimes little hairy laminae. The eyes vary as to 

 size; in some species they are very small. 



The thorax presents four stigmata, two anterior and two posterior. 



The wings are always distant and accompanied by halteres. Their edge is 

 more or less fringed with cilia. The skin of the abdomen is formed of a con- 

 tinuous membrane, so that this part of the body is susceptible of being dis- 

 tended and of acquiring a considerable volume, as necessarily happens in those 

 female Hippoboscsp, where the larvae are hatched and continue to reside until 

 the period of their transformation into pupae. At this epoch the larvae are 

 produced in the form of a soft, white egg, almost as bulky as the maternal 

 abdomen; the skin hardens and becomes a firm shell, at first brown, then 

 black, round, and frequently emarginated at one end, and presenting a glossy 

 plate or operculum which is finally detached in the manner of a cap to allow 

 the egress of the perfect insect. 



These insects, which have been called by some authors Mouches-Araignees, 

 live exclusively on quadrupeds or birds, run very fast, and frequently 

 sideways. 



Some Coriaces, Lat., have a very distinct head articulated with the 

 anterior extremity of the thorax. They form the genus 



HIPPOBOSCA, Linnaeus, Fabricius. 



The Hippobosca proper is furnished with wings ; and has very distinct eyes 

 occupying all the sides of the head ; antennae in the form of tubercles, with 

 three setae on the back. 



H. equina, Lin. Brown mixed with yellowish. Found on horses and 

 oxen, usually under their tail. 



There are other subgenera. 



The head of the other Pupipara Phthiromyies, Lat., is very small or almost 

 wanting. It forms a minute, vertical body near the anterior and dorsal 

 extremity of the thorax. 



They constitute the genus 



NYCTERIBIA, Lalreille. 



These insects have neither wings nor halteres, and resemble spiders still more 

 than the preceding ones. They live on bats. Linnseus arranged one species, 

 and the only one he knew, with the Pediculi. 



