INTERNAL ANATOMY OF INSECTS. 51 
of this structure, can be selected, than the gnat (Culex L.). 
You must have occasionally observed in tubs of rain- 
water, numerous little wriggling worm-like animals, which 
frequently ascend to the surface; there remain a while, 
and then bending their head under the body rapidly 
sink to the bottom again. These are the Jarvee of some 
species of the genus just named; and if you take one out 
of the water and examine it, you will perceive that it is 
furnished near the end of its body with a singular organ, 
which varies in length according to the species, and forms 
an angle with the last segment but one*. The mouth of 
this organ is tunnel-shaped, and terminates in five points 
like a star; and by this it is usually suspended at the sur- 
face of the water, and preserves its communication with 
the atmosphere: in its interior is a tube which is ccn- 
nected with the ¢rachee, and terminates in several open- 
ings, visible under a microscope, at the mouth of the or- 
gan. ‘The points or rays of the mouth when the animal 
is disposed to sink in the water, are used to close it, and 
cut off its communication with the atmosphere. When 
the animal is immersed, a globule of air remains at- 
tached to the end of the tube, so that it is in fact of less 
specific gravity than that element, and it is not without 
some effort that it descends to the bottom; but when it 
wishes to rise again, it has only to unclose the tube, 
and it rises without an effort to the surface, and remains 
suspended for any length of time. Its anal extremity is 
clothed with bunches of hairs, which are furnished with 
some repellent material which prevents their becoming 
wet”: it is this repellent quality that probably causes a 
2 Prater XIX. Fic. 9. a. > Thid. 6. 
Bee 
