NO. 8 ANATOMICAL LIFE OF THE MOSQUITO SNODGRASS 49 



forming a bubble at the base of the proboscis. This air is then 

 pumped into the stomach as a long narrow bubble that extends back to 

 the fourth abdominal segment. Pressure by the distended abdomen 

 now pushes the thorax forward until it ruptures the pupal cuticle in 

 a median slit along the back from the neck to the end of the meso- 

 thorax. Outside air then enters the cleft and is rapidly swallowed, 

 going back in the stomach as far as the sixth abdominal segment and 

 greatly distending the abdomen. Knab (1909), in describing the role 

 of air in the ecdysis of insects, says of the mosquito that on emergence 

 from the pupa it is distended with air far beyond its natural size, the 

 integument being stretched to its utmost. According to the writer's 

 observations on emerging mosquitoes the degree of distention is highly 

 variable, even with individuals of the same species. 



Pupae of Aedes aegypti, before the adult ecdysis, are observed to 

 have the abdomen extended straight back from the thorax, and during 

 the emergence it is held, or floats, in this position with the tail fins 

 against the water surface (fig. 18 A). When the pupal cuticle splits on 

 the back of the thorax, the thorax of the adult bulges out and pushes 

 apart the lips of the cleft. This produces a transverse split over the 

 back of the pupal head, so that the pupal skin can now be widely 

 opened anteriorly (B) to allow the egress of the adult. At the same 

 time the cuticle on top of the pupal head between the eyes breaks 

 out and folds forward as a free flap beyond the antennal bases (A,B). 

 Behind the antennae the anterior tentorial arms project internally as 

 a pair of slender tapering rods (B). 



Inasmuch as the legs of the adult, as well as the wings and mouth 

 parts, are enclosed in tight-fitting pupal sheaths, the mosquito cannot 

 use its appendages for freeing itself. Yet, when the head and thorax 

 are free, the abdomen follows and the entire adult slowly rises verti- 

 cally from the pupal skin as if pushed out from below. The legs and 

 wings are at first closely pressed against the body, but as the legs 

 are freed they at once become active, and appear to be reaching for 

 the surface of the water. The mosquito seems to know instinctively 

 that now and henceforth it must support itself on its legs. It will be 

 noted that the legs of the emerged adult are greatly longer than their 

 pupal sheaths ; the hindleg of an Aedes (fig. 17 B), for example, may 

 lengthen to two and a half times the length of the corresponding folded 

 leg of the pupa (A). When the end of the abdomen and the wings 

 are finally out of the pupal thorax and the legs are all free, the new 

 insect confidently steps out onto the surface of the water and calmly 

 walks away from the discarded pupal skin. It may come to rest on 



