40 
remaining at the surface of the water, feeding, as before, upon floating 
particles for some time, it would wriggle violently and descend to the 
bottom, where it would remain frequently as long as two minutes 
before reascending to the top. Its appetite was evidently so great 
that it was not satisfied with the floating particles, and when it descended 
to the bottom it mouthed the particles of sand, evidently swallowing 
the slime on the little stones and frequently even picking up quite a 
a large sand pebble and then dropping it again. In this stage the indi- 
vidual which grew most rapidly remained only four days, and trans- 
formed to pupa on the morning of the 17th, after a larval existence of 
sixteen days. The accompanying figures of the larve have been drawn 
with such care that detailed description will be unnecessary. They 
were drawn from life under the compound microscope. Some of the 
structures are puzzling, notably the organs occuring on the dorsum of 
the abdominal segments, shown most plainly in fig. 15, and which look 
as though they might be spiracles until they are examined under a high 
power in the cast skin. The writer does not care to risk an expression — 
of opinion as to their function, although possibly it is known, and they 
possibly occur in other aquatic dipterous larve. In the early stages of 
the larve they resemble minute branchial tufts, but no tracheal con- 
nection has been found. 
THE pupa.—The accompanying figure (fig. 16) well represents the 
Fic. 16.—Pupa of Culex pungens at left; pupa of Anopheles quadrimaculatus at right—greatly enlarged 
(original). 
differences between the pupa of Culex and that of Anopheles. In this 
stage the insects of the two genera are not so markedly different as in 
the larval stage. Structural differences need not be described, as they 
are sufficiently shown in the illustration. The eye will at once be 
caught by the difference in position, the pupa of Culex resting in a 
more perpendicular attitude than that of Anopheles, and the marked 
difference in shape between the respiratory siphons, which issue from 
the thorax instead of from the anal end of the abdomen, will at once 
