88 MOSQUITOES OF NORTH AMERICA 



on its final ovate form. The accessory eye is short and broad, at first separated 

 somewhat from the main eye, later partly covered by it. In young pupge one can 

 distinguish three darkly pigmented portions in it, later it becomes entirely 

 black." 



Easchke states that the accessory eye has an outer transparent gelatinous 

 layer; out of the pigment mass projects a single crystalline column. The cornea 

 of the main eye is represented by a smooth layer of crystalline hypodermal cells. 

 The lateral parts of the supraoesophageal ganglion send large nerve trunks to 

 the main eyes and these each send out a branch to the accessory eyes. 



Similar to what Weismann has shown in the larva of Chaol)oru& a kind of 

 regressive metamorphosis takes place in the accessory eye, while the main eye be- 

 comes highly developed. Nevertheless the accessory eye persists in the imago as 

 a pigment spot, but it is hidden by the scale-covering of that part of the head. 



Eadl has shown that in Arthropods the compound eyes are developed from two 

 foci ; in the course of development both of these may unite to form the eye, or 

 one of them may be wholly or partly suppressed. The latter is the condition in 

 the Culicidas and other Nemocera. 



THE THORAX. 



The thorax consists of the fused first three segments of the body, and its 

 integument is membranous. It is broad and somewhat flattened, broadest at the 

 middle, and without prominent angles. There are hairs present, mostly long, 

 along the anterior and lateral margins ; these show a definite arrangement and 

 indicate the three elements of the thorax. At the middle and hind angles there 

 are large fan-shaped tufts of ciliate hairs with a common base. These hinge, to 

 bend forward, upon low tubercles, and are prevented from bending backward by 

 a small chitinous plate. 



THE ABDOMEN. 



The abdomen is long, slender and cylindrical and consists of nine well-defined 

 segments. The integument of all but the ninth is entirely membranous. The 

 divisions of the segments are marked by constrictions and the integument is 

 more delicate and flexible in that region. The first seven segments are alike in 

 character but differ in size, the anterior ones being much shorter and the 

 seventh much the longest. The first six segments bear lateral groups of long 

 hairs ; the hairs in the groups of the first two segments are more numerous than 

 in the succeeding ones and are curved and stouter. In addition to the larger 

 lateral hairs there are other smaller hairs, singly and in groups, which form 

 various series, lateral, dorsal and ventral. 



The eighth segment is shorter than the preceding ones and bears dorsally 

 the chitinous respiratory tube. At the apex of the tube is the opening through 

 which the larva takes air into its tracheae. The tube can be closed by a set of 

 flaps and these, with their mechanism, will be described later. Close to the apex 

 of the tube, dorso-laterally, are a pair of small movable spines. Basally on the 

 tube are a pair of ventro-lateral longitudinal series of dentate flattened spines 

 which point obliquely backward. These have been termed the pecten. At 



