37 
specific gravity seems greater than that of water, so that it reaches the 
surface only by an effort, and the writer has already pointed out in the 
ease of C. pungens that when the larva becomes enfeebled and is not 
strong enough to wriggle up to the surface it drowns. Feeding as it 
does at the bottom upon the heavier particles which sink, its specific 
gravity is explained. The larva of Anopheles quadrimaculatus, how- 
ever, habitually remains at the surface of the water. Its breathing 
tube is very much shorter than that of Culex and its body is held not 
at an angle at the surface, but practically parallel with the surface and 
immediately below the surface film, so that portions of its head, as 
well as its breathing tube, are practically out of the water. Its head 
rotates upon its neck in a most extraordinary way, so that the larva 
i 
T \ 
reve ee 
oe ie 
Fic. 13.—Anopheles quadrimaculatus and Culex pungens: Half-grown larva at left and in center, in 
comparison with half-grown larva of Culex pungens at right (figure at left has been cleared)— 
greatly enlarged (original). 
can turn it completely around with the utmost ease and feeds habitu- 
ally with the under side of the head toward the surface of the water, 
whereas the upper side of the body is toward the surface. In this cus- 
tomary resting position the mouth parts are working violently, the 
long fringes of the mouth parts causing a constant current toward the 
mouth of particles floating on the surface of the water in the neigh- 
borhood, which thus gradually converge to this miniature maelstrom 
and enter the alimentary canal. The spores of alge, bits of dust, 
minute sticks, bits of cast larval skins, everything in fact which floats, 
follow this course, and, watching the larva under the microscope, they 
can plainly be seen to pass through the head into the thorax until they 
