32 MOSQUITOES OF NORTH AMERICA 
“The tracheal system is somewhat complicated and very variable. In general 
the antenna is supplied by a large tracheal trunk which is present upon both 
sides of the head. This generally throws off a branch, which, passing towards 
the median side of the antennal nerve, enters the antenna and in its course sends 
out a number of branches to the large nerve. Another somewhat larger trunk 
passes along the lateral side of the nerve-trunk as continuation of the main 
trunk, probably also throws off branches to the antennal nerve and can also be 
traced into the antenna. At the base of the second segment both trunks divide 
into several branches; some of them pass between the ganglionic layer and the 
hypodermis and divide further, while others penetrate the ‘ nerve-funnel’ and 
supply the central parts of the organ. At least one of these continues through 
the opening in the central plate into the shaft of the antenna. 
“ Beneath the central plate there is a space through which the trachee and the 
nerve cords pass. This space is enclosed at the sides by the ‘ nerve-funnel,’ the 
layer of ganglion cells and the rods, as well as by some less differentiated cells 
(fig. 1, W) which represent transition states between the rod-cells and hypo- 
dermis (H’) lying beneath the plate; anteriorly the hollow space is limited by 
the plate and the hypodermal layer pertaining to it. It is connected, through 
the opening in the plate, with the interior space of the shaft as well as with the 
radial spaces between the groups of rods and in consequence it is also connected 
with the outer space between the hypodermis and the layer of ganglionic cells; 
during life it is filled with blood fluid. 
“The essential among the elements of this highly developed sense-organ are 
then the rods, which are, as will be shown in the following, modified hypodermal 
cells. The remarkable size of the organ and the great number of sensory termi- 
nal elements, as well as the large nerve-trunk in immediate connection with the 
cerebral ganglion, point to a function of great importance in the life of the 
insect or the preservation of the species.” 
In the female the antenna is more simple and the sensory organ is much 
smaller and less complicated. 
“ The part corresponding to the plate of the male consists of a circular plate 
of cuticular substance surrounding the base of the shaft. Here it is clearly 
apparent that the plate is nothing but the connecting membrane, and the plate 
of the male is without doubt homologous with that of the female, only developed 
to a much higher degree. . . . The rods are in every respect similar to those of 
the male, of the same size, and also connected with the ganglion cells by fine 
fibers. Their mode of termination is, however, a different one than in the male. 
The plate in this case does not possess any processes but the rods terminate 
with their apices in the substance of the plate itself, and, to be more exact, 
between the chitinous ring and the base of the shaft. Upon the median and 
lateral surfaces of the rod-layer lie elongate, less differentiated cells representing 
intermediate stages between the rods and the ordinary hypodermal cells.” 
Child gives the following comparison of Culex pipiens with Corethra: 
1. Male: 
“The antenna of the Culex male shows great similarity with that of Moch- 
lonyz. . . . The basal segment is here also rudimentary, somewhat sunken into 
the head and serves as point of attachment for the antennal muscles. 
“The second segment is a comparatively large, cup-shaped organ, the relation 
of which to the other segments, and its structure, are in general the same as in 
Mochlonyz, so that I do not need to give a separate figure; I only wish to men- 
tion a few points in which the two forms differ from each other. The entire 
segment measures 0.17 mm. in length and 0.12 mm. in breadth, therefore is 
