56 CULICID^ [CH. VII 



Internal anatomy. The internal anatomy of the Culicids 

 is very constant and the following description of Anopheles 

 maculipennis will apply, with but slight modifications, to any 

 other member of the family. This example has been selected 

 since it has been minutely described by Nuttall and Shipley, 

 from whose account the present description is largely taken. 



{a) Digestive organs. According to the above-mentioned 

 authors the alimentary canal may be divided into eleven parts as 

 follows : mouth ; buccal cavity ; pharynx or pumping organ ; 

 oesophagus, with which are connected three diverticula, two 

 dorsal and one ventral ; oesophageal valve ; mid-gut ; ileum ; 

 colon ; rectum ; and anus. 



The mouth is that region where the various mouth-parts 

 coalesce and is of no special interest. The buccal cavity extends 

 from the mouth to a valvular arrangement situated at the com- 

 mencement of the pharynx. It is lined with chitin throughout, 

 that of the ifoor being much stouter than that of the roof, 

 which forms a kind of soft palate capable of being raised or 

 depressed by means of muscles. Accordingly the size of the 

 buccal cavity can be increased by these means and it may 

 at times assist in suction. At the junction of the buccal cavity 

 and pharynx is situated a valvular apparatus, formed by a 

 double row of chitinous hairs attached to the ventral surface. 

 These hairs, in addition to acting as a valve, may also serve 

 as a kind of filter and keep out large particles. 



The pharynx, or pumping organ, extends from this valve 

 to the commencement of the oesophagus, and consists of a 

 thick-walled tube composed of three longitudinal, chitinous 

 plates, conjoined by a fold of chitin at their margins. The 

 lumen of the tube is triangular in shape, and powerful 

 muscles, arising from each of the three chitinous plates and 

 attached to the exoskeleton, serve to separate the walls and 

 increase the capacity of the pharynx. By means of the power- 

 ful pharyngeal muscles, which almost fill the head of the 

 mosquito, the insect is enabled to suck up hquids into its 

 pharynx, and after the relaxation of the muscles the walls 

 contract again, by virtue of the elasticity of the chitinous 

 supporting plates. Any ingested liquid is thus forced out of 



