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 

 h3rpodermis 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 tracheae 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 Cuhx pipiens with Corethra: 



1. Male: 



" The antenna of the Culex male shows great similarity with that of Moch- 

 lonyx. . . . 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 

 Moclilonyx, 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 0.13 mm. in breadth, therefore is 



