5 86 The American Naturalist. [July, 
ous effects upon horses and dogs, though only annoying to man. 
Very recently another species of the tsetse-fly has been dis- 
covered in Austraha, with similar " poisonous and pestilential " 
habits. A genus allied to Stomoxys is ascribed to South America, 
though I know nothing further concerning it. 
Among the diptera we have a number of families of widely 
different structure and habits that subsist, either wholly or in 
part, upon the blood of mammals, including the mosquitoes 
(Culicidai), with about one hundred and fifty known species, 
scattered over a large part of the world, the Simuliidae, with the 
Buffalo gnat, and about sixty other widely-distributed species, the 
horse-flies (Tabanidae), with over thirteen hundred known species, 
the score or two of species of Stomoxyin^, and a few species of 
Chironomidai and Leptidas. In all these flies it is the female 
only that draws blood, and they all seem to have the ability to 
emit a poisonous saliva into the wound they make, in some of a 
more irritating nature than others. The males, in general, are 
harmless, lounging fellows, with a proboscis weaker than in the 
female, used in sipping nectar from flowers, or the sweet sap of 
plants. They are not so commonly found as the females, and of 
the tsetse-fly are still unknown. Hcematobia serrata has habits 
very similar to those of Stomoxys, as stated in Insect Life. 
The eggs are deposited in fresh cow manure, and only twelve 
days are required for the insect to acquire its adult condition. 
What its future in America will be one cannot say ; there can be 
but little doubt, however, that it will soon spread over the entire 
United States. 
It is very probable that the largest number of cosmopolitan 
insects are found among the Diptera. Reasons therefor we can 
readily find; they furnish the greater number of our domestic 
pests, and their eggs or larvae are constantly mingled with our 
food material, or common objects of commerce. Indeed, the won- 
der is not that there are so many species that follow man in his 
colonizations and migrations, but that the number is so few. 
Musca domestica, that inseparable companion of man, is believed 
to occur everywhere about his dwellings; even on the unin- 
habited plains of America it abounds, as Professor Snow has 
