40 



remaining at the surface of the water, feeding, as before, upon floating 

 particles for some time, it would wriggle violentl}^ 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 gieat 

 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 larva? 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 

 possiblj^ occur in other aquatic dipterous larvte. In the early stages of 

 the larvffi the}^ resemble minute branchial tufts, but no tracheal con- 

 nection has been found. 



The pupa. — The accompanying fig'ure (fig. 16) well represents the 



Fig. 16. — Pupa of Calc.r jiniii/^ina at left; pupa of Anopheles q^iadrimaculatus at rijrht — ^greatly enlarged 



(original). 



diflferences between the pupa of Culex and that of Anopheles. In this 

 stage the insects of the two genera are not so markedly difi^erent as in 

 the larval stage. Structural difi'erences need not be described, as they 

 are suflficiently shown in the illustration. The eye will at once be 

 caught by the difi'erence 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, Avhich issue from 

 the thorax instead of from the anal end of the abdomen, will at once 



