342 DIVISION III. ARTICULATED AMIMALS.—CLASS IV. INSECTA. 
it look fat. The fat is of a greenish-yellow color, and of an oily consis- 
tence. All the muscles are flabby, and the heart often so soft that the 
fingers may be made to meet through it. The lungs and liver partake of 
the disease. The stomach and bowels are pale and empty, and the gall- 
bladder is distended with bile. These symptoms seem to indicate, what is 
probably the case, a poison in the blood, the germ of which enters when 
the proboscis is inserted to draw blood. The poison-germ contained in a 
bulb at the root of the proboscis seems capable, although very minute in 
quantity, of reproducing itself. The blood after death by Tsetse is very 
small in quantity, and scarcely stains the hands in dissection. 
“The mule, ass, and goat enjoy the same immunity from the Tsetse as 
man and the game. Many large tribes on the Zambesi can keep no domes- 
tic animals except the goat, in consequence of the scourge existing in their 
country. Our children were frequently bitten, yet suffered no harm; and 
we saw around us numbers of zebras, buffaloes, pigs, pallahs, and other 
antelopes, feeding quietly in the very habitat of the Tsetse, yet as undis- 
turbed by its bite as oxen are when they first receive the fatal poison. 
There is not so much difference in the natures of the horse and zebra, the 
buffalo and ox, the sheep and the antelope, as to afford any satisfactory ex- 
planation of the phenomenon. Is a man not as much a domestic animal as 
a dog? 
“The curious feature in the case, that dogs perish though fed on milk, 
whereas the calves escape so long as they continue sucking, made us imagine 
that the mischief might be produced by some plant in the locality, and not 
by Tsetse; but Major Vardon, of the Madras army, settled that point by 
riding a horse up to a small hill infested by the insect, without allowing him 
time to graze; and, though he only remained long enough to take a view 
of the country and catch some specimens of Tsetse on the animal, in ten 
days afterwards the horse was dead.” 
The fifth family of Diptera —-Athericea —comprises the genera Syrphus, 
@strus, Conops, and Musca. , 
Syrpuus. — This group is separated into a large number of subgenera, 
the most remarkable of which are Syrphus proper, Vermidlio, and Volu- 
cella. The Syrphi have the abdomen narrowed from the base to the apex. 
Their larve feed solely upon aphides, which they often hold up in the air, 
and suck with great rapidity. 
Vermiiio. — This insect has a white face; its forehead gray, bordered 
with black; the thorax of a yellowish-gray, with four brown stripes in the 
male; the abdomen light yellow, spotted with black ; and the wings glassy. 
The larva of the Vermilio has a thin, cylindrical body, capable of bending 
itself in every direction ; a conical head, armed with two horny points; and 
