THE ANATOMY OF THE ADULT MOSQUITO 87 



rnent of the sort is a physiological necessity, as it would 

 be quite impossible for the saliva to be forced down a tube 

 while the food is being drawn up through it. 



When the Mosquito brings the proboscis into action to 

 pierce the cuticle of the plant or animal from which it seeks 

 its food, all these parts, except the sheathing labium, are 

 forced into it, while the labium is bent down into a sort 

 of loop which progressively narrows as the piercing organs 

 penetrate more and more deeply. On either side of the 

 base of the proboscis may be seen a pair of jointed appen- 

 dages, the maxillary palpi. These organs have been 

 described by several authorities as labial palps, but a closer 

 examination shows that they are really connected with the 

 base of the maxillary lancets through the intermediation of 

 a piece which, in the usual position of the parts, is hidden 

 within the base of the labium. In most cases the palpi 

 consist of five visible joints, but they present great sexual 

 and generic differences within the family, and require 

 especial notice in systematic work, as the classification of 

 these insects is largely based on their characteristics. 



In some species they greatly exceed the proboscis in 

 length, while in the genus Mdes they are quite rudimentary 

 in both sexes and appear to consist of only a single short 

 joint. 



The head is connected with the thorax by a soft flexible 

 neck corresponding in function to the intersegmental mem- 

 branes of the abdomen, though by some authorities it is 

 considered as a part of the prothorax, which allows of 

 a considerable freedom of movement between these two 

 divisions of the body. 



The thorax is the most bulky portion of the body, as, 

 though but little broader than the head, it is more than 

 twice as deep. It is composed of three segments, but the 

 great preponderance of the middle of the three, or meso- 

 thorax, and the fact that the three are fused together into 

 a single rigid mass, makes it not altogether easy to make 

 out the lines of division between the component parts. 

 Viewed from above, almost all that is visible is the tergum of 

 the mesothorax, but in some mosquitoes, as in Psorophora, 



