37 



speeitic gra\ity seems gTeater than that of water, so that it reaches the 

 surface only hy an effort, and the writer has already pointed out in the 

 case of C. pun gens that when the larva becomes enfeebled and is not 

 strong- enough to wriggle up to the surface it drowns. Feeding as it 

 docs at the bottom upon the heavier particles which sink, its specific 

 gravity is explained. The larva of AnopJieles qaadrmiacidatus^ how- 

 ever, habitually lemains 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 

 111 as its breathing tube, are practically out of the water. Its head 

 rotates upon its neck in a most extraordinar}' wa}', so that the larva 



Fig. 13. — Anopheles quadriinaculatus 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- 

 all}^ 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 (pausing 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 algie, bits of dust, 

 minute sticks, bits of cast larval skins, ever5'thing 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 



