DIPTERA, 383 
comes 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. This shell has no annuli or transverse inci- 
sures, a character which distinguishes it from the other pupz of 
Diptera, and from those of the Athericera particularly, to which it 
approximates the most. 
It is to the splendid Memoirs relative to these Insects by Reau- 
mur, De Geer, and M. Leon Dufour, all accompanied by detailed 
figures, that we must recur, in order to obtain a profound knowledge 
of these transformations, and an explanation of the changes which 
take place in the female at the moment of depositing her larve. 
The latter, in particular, has surpassed his predecessors by anatomi- 
cal investigations which have unveiled some highly interesting and 
curious facts, such as the existence of salivary glands, of a sort of 
matrix * consisting of a large, musculo-membranous pouch, adapted 
for gestation and analogous to the uterus of woman, and of ovaries 
entirely different from those of other Insects. These ovaries consist 
of two obtuse, ovoid bodies filled with a white homogeneous pulp 
free and rounded at one extremity and terminating at the other in 
a peculiar duct. According to this anatomist these ovaries closely 
approximate to those of woman in their form and position; Reau- 
mur had a glimpse of them, The matrix, which at firstis very small, 
by the progress of gestation becomes enormously dilated, pushes back 
the viscera, and finally invades the whole cavity of the abdomen, 
which is thus rendered very large. The memoir of this able obser- 
ver presents other interesting facts, which, as they differ but little, if 
at all, from the ordinary laws, we shall not stop to analyze. 
These Insects, which have been called by some authors Mouches- 
Araignees, live exclusively on Quadrupeds or Birds, run very fast, 
and frequently sideways. 
Some—Crortaces, Lat. + — have a very distinct head articulated 
with the anterior extremity of the thorax. They form the genus 
; Hirrososca, Lin., Fab. 
Hirpososca, proper. 
Furnished with wings; very distinct eyes occupying all the sides 
of the head; antenne in the form of tubercles, with three sete on the 
back. 
* Professor Nitzsch, who, in his Memoir on Epizoic Insects, treats of various 
genera of Pupipara, mentions two ovaries and four biliary vessels in Hippobosca, 
but he neither alludes #o this matrix nor to the salivary glands. 
+ Dr. Leach has published a Monograph of these Insects, enriched with excellent 
figures, beautifully engraved. 
