24 



The larvw issue from th(^ underside of the ego- masses, and are 

 extreme]}' active at birth. When first ol)served it is easj- to fall Into 

 an error regarding- the length of time which they can remain under 

 water, or rather without coming to the surface to breathe, since, in 

 striving to come to the surface for air, man}' of them will strike the 

 underside of the egg mass and remain there for many minutes. It is 

 altogether likely, however, that they get air at this point through the 

 eggs or through the air film by which the egg mass is surrounded, and 

 that they are as readily drowned by continuous immersion as are the 

 older ones, as will be shown later. 



One of the first peculiarities whicli strikes one on observing these 

 newlj'-hatched larvse under the lens is that the tufts of filaments which 

 are conspicuous at the mouth are in absolutely constant vibration. This 

 peculiarity, and the wriggling of the larvae through the water, and 



FiG.-2.—Culex2JUugcns: Head of larva from below id left; .same Inmi above iit right— greatly enlarged 



(original). 



their great activity, render them interesting objects of study. In gen- 

 eral the larv;v% passing through appai'ently three different stages, reach 

 maturity and transform to pupw in a minimum of seven days. When 

 nearly full grown, their movements were studied with more care, as 

 they were easier to observe than when newly hatched. At this time 

 the larva remains near the surface of the water, with its respiratory 

 siphon at the exact surface and its mouth filaments in constant vil>ra- 

 tion, directing food into the mouth cavity. Occasionally the larva 

 d(\scends to the liottom, }jut, though I'epeatedly timed, a healthy indi- 

 vidual was never seen to remain voluntarilv below the surface more 

 than a minute. In ascending it comes up with an efl'ort, with a series 

 of jerks and wrigglings with its tail. It descends without efl'ort, but 

 ascends with difliculty; in other words, its specific gravity seems to be 

 greatei- than that of the water. As soon, how'ever, as the respiratory 



