THE ANATOMY OF THE ADULT MOSQUITO 79 



In this region of the body no sign of segmentation can 

 be made out, nor is there any visible separation between the 

 dorsal and ventral chitinous shields, such as is found in the 

 other regions of the body. 



The greater part of the sides and front of the head are 

 occupied by the facetted eyes. These are always large and 

 well developed and in certain species may even touch each 

 other in front and nearly so below. Their anterior border 

 is usually somewhat hollowed back to lodge the bases of 

 the antennae, so that they tend to a reniform outline. 

 There are no ocelli, or simple eyes, such as are found in 

 the majority of Diptera, and though some authorities assert 

 that they are present in a rudimentary form, I have not 

 been able to satisfy myself as to the existence of anj^ trace 

 of them in the adult insect, and for practical purposes, at 

 any rate, they may be considered as absent. 



Immediately in front of the eyes will be seen the 

 antennae. These are of the moniliform type, and although 

 of fundamentally similar construction, differ greatly in 

 appearance in the two sexes, owing to the organ in the 

 male being so richly provided with long, silky hairs as to 

 form a pair of singularly beautiful plumes ; while in the 

 female these hairs are less numerous and down-like, so that 

 the joints of the antennae itself are plainly visible, and are 

 the portion of the organ that catches the eye. In both sexes 

 the antennae is typically formed of fourteen joints, the basal 

 one of which is much the largest and of globular form, the 

 constriction at its base being almost fused with the cephalic 

 shield so as to be capable of little motion. The greater 

 part of the front of this large basal joint is occupied by a 

 soft but tightly stretched membrane, and into the centre 

 of this is articulated the base of the second joint, which, like 

 those that follow it, though but little shorter, is not one- 

 fifth of the diameter of the basal joint. The chitinous wall 

 of the latter is grooved on its interior for a richly-developed 

 system of nerve threads, which are symmetrically arranged 

 in its lining membrane like the wires of a birdcage. The 

 structure of this joint has been described in great detail by 

 Dr. Christopher Johnstone of Baltimore {U.S. Quart. Journ. 



