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 pupe one can 
distinguish three darkly pigmented portions in it, later it becomes entirely 
black.” 
Raschke 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 supracesophageal 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 Chaoborus 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. 
Radl 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 Culicide 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 trachee. 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 
