496 INSECTA. 



The thorax presents four stigmata, two anterior and two poste- 

 rior. 



The wings are always distant and accon)panied by halteres. 

 Their edge is more or less fringed with cilia. The skin of the ab- 

 domen is formed of a continuous membrane, so that this part of the 

 body is susceptible of being distended and of acquiring a conside- 

 rable volume, as necessarily happens in those female Hippoboscae, 

 where the larvas are hatched and continue to reside until the period of 

 their transformation into pupae. At this epoch the larvae are pro- 

 duced in the form of a soft, white egg^ almost as bulky as the ma- 

 ternal 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, Lin. Fab. 

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

 occupying all the sides of the head; antennse in the form of tubercles, 

 with three setsc on the back. 



H. equina, L. Brown mixed with yellowish. Found on Horses and 

 Oxen, usually under their tail. 



There are other subgenera. 



The head of the other Pupipara — Phtkiromyies, 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 



NycTEKiBiA, Lat. 

 These Insects have neither wings nor halteres, and resemble Spiders still 

 more than the preceding ones. They live on Bats. Linnxus arranged one 

 species, and the only one he knew, with the Pediculi. 



