58 CULICIDiE [CH. 



the pharynx into the next region of the ahmentary canal. 

 The pharynx of the female mosquito is both larger and stronger 

 than that of the male, this being the result of the more voracious 

 habits of the former. 



The oesophagus is a short, circular tube, extending from the 

 posterior end of the tri-radiate pharynx to the oesophageal valve. 



Into its posterior end, about on the level of the origin of 

 the first pair of legs, open the three oesophageal diverticula. 

 The largest of these is the ventral diverticulum opening into 

 the oesophagus by means of a single median pore and extend- 

 ing backwards beneath the alimentary canal as far as the 

 sixth or seventh segment. The other two dorso-lateral diver- 

 ticula are much smaller and open one on each side of the 

 oesophagus. 



The function of these sacs is still far from being settled, 

 for although Nuttall and Shipley have shewn that food material 

 is passed into them, yet it is doubtful whether their chief 

 function is to serve as reservoirs. 



The sacs generally contain small bubbles of carbon dioxide 

 and also larger or smaller numbers of a small round fungus 

 belonging to the Entomophtoraceae. 



The presence of these bubbles in the sacs has caused certain 

 authors to suppose that there was some connection between 

 them and the tracheal system, whilst others, noticing the 

 rhythmic contractions of the ventral sac, have supposed that 

 it was an accessory pumping apparatus. The main function 

 of the diverticula is probably to assist in the feeding of the 

 mosquito and the manner in which this is affected will be 

 described later {vide habits). 



The oesophageal valve is homologous with the proventriculus 

 of many insects, and serves as a valve between the oesophagus 

 and the mid-gut. It is little more than a slight invagination 

 of the intestinal wall surrounded by a very thick sphincter 

 muscle. Six small protuberances, the remnants of the caecal 

 appendages of the larva, can usually be seen in the walls of 

 the valve. 



The mid-gut is the only part of the alimentary canal that 

 is not lined with chitin and consequently the only part in which 



