76 MOSQUITOES OF NORTH AMERICA 
the supra and infra-cesophageal ganglia and their commissures. At first it is 
narrow, but posteriorly becomes a large chamber (the pumping organ). 
“The pumping organ occupies with its muscles a large portion of the head 
behind the level of the cerebral ganglia. In the state of rest its lumen is tri- 
radiate in transverse section. The walls are formed of three large and thick 
chitinous plates, one placed on either side, and one superiorly. Into each of 
these plates powerful muscles are inserted. The plates are connected by thin 
non-chitinous membrane, and their edges are rolled so that they form a spring 
capable of returning to their original position so soon as the separating force of 
the muscles ceases. 
“ Posteriorly, where the pharynx becomes very narrow, a sharp bend occurs 
and a valvular action is produced. The whole forms a very powerful suctorial 
apparatus. 
“The Gsophagus—Immediately beyond the pumping organ the chitinous 
layer ceases, and the rest of the fore-gut is formed of excessively thin membrane. 
At the junction of the two portions a sharp bend occurs, and the floor projects 
so as to form a valvular flap. 
“The thin-walled cesophagus is a large dilated sac, whose walls are supported 
by surrounding structures. Into the posterior wall of the dilated and thin- 
walled cesophagus projects the papilla-like anterior portion of the mid-gut. 
“The Dwwerticula of the @sophagus—From the cesophagus two or three 
diverticula, similar in nature to the cesophagus, extend backwards. Of these, 
one is of great size, and usually contains gas bubbles. This usually extends into 
the abdomen, and is a prominent object in dissections and sections. 
“ The Homologue of the Proventriculus.—There is no true proventriculus as 
in many insects. There is, however, an interesting fold of the fore-gut into the 
mid-gut which represents this organ. The muscular bundles are here increased, 
and the whole forms a valvular muscular organ. 
“The Mechanism of Feeding.—The powerful pumping action which must 
result from a drawing asunder of the three large chitinous plates of the pumping 
organ is very evident. These plates, also, when drawn apart must, by reason of 
their spring-like shape, revert to their original positions close together, without 
any muscular aid. Posteriorly the valve-like arrangement mentioned before 
prevents regurgitation. Further, when the blood reaches the junction of the 
cesophagus and mid-gut the invaginated portion is withdrawn, and is distended 
by the entering blood into a distinct ‘ crop,’ the valvular function is suspended, 
and the blood flows onward. 
“ The Mid-gut—The mid-gut extends from the proventriculus to the origin 
of the malpighian tubes. 
“The anterior narrow portion of the mid-gut lies in the thorax, and does not 
become distended with blood. The posterior portion when fully dilated fills the 
greater portion of the abdomen, the viscera being pushed into the last few 
segments. 
“ The Hind-gut.—The hind-gut is short and passes in one or two bends from 
the pylorus to the anus. Immediately beyond the pylorus there is a considerable 
dilatation which is poorly supplied with muscular fibres: into this open the five 
malpighian tubules. For a short distance beyond this the lumen is narrow 
(ileum), but becomes gradually larger (colon). At the termination of the colon 
there is a slight constriction, after which the canal dilates again to form the 
rectum. 
“ Into the rectum project six solid growths, the so-called rectal glands, which 
are, however, papilla. Posteriorly the rectum ends in the anus close above the 
genital canal. 
