131 



The thin-walled oesophagus is a large dilated 

 sac, whose -walls are supported by surrounding 

 structures. Into the posterior wall of the dilated 

 and thin-walled oesophagus projects the papilla- 

 like anterior portion of the mid-gut. 



The Diverticula of the Oesophagus. — From the 

 oesophagus two or three diverticula, similar in 

 nature to the oesophagus, extend backwards. Of 

 these, one is of great size, and usually contains 

 gas. This most usually extends into the abdo- 

 men, and is a prominent object in dissections and 

 sections. In the newly-hatched mosquito it is 

 small, but rapidly becomes large enough to extend 

 into the abdomen (Fig. 30). 



The Homologue of the Proventiculus. — There is 

 no true proventri cuius 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 (Fig. 30). 



The Mechanism of Feeding. — The powerful 

 pumping action which must result from a draw- 

 ing 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 posi- 

 tions close together, without any muscular aid. 

 Posteriorly the valve- like arrangement mentioned 

 before prevents regurgitation. Further, when the 

 blood reaches the junction of the oesophagus and 

 mid-gut the invaginated portion is withdrawn, 

 and is distended by the entering blood into a dis- 

 tinct ' crop.' The valvular function is suspended 

 and the blood flows onward. 



The Mid-gut. — The mid-gut extends from th 



