48 GNATS OK MOSQUITOES— CHAPTER III 



structure, and from its inner and posterior corner there 

 projects a short, three-jointed maxillary palp in the form of 

 a truncated cone, the extremity of which is armed with 

 minute spines. The above description should suffice to 

 enable the dissector to recognise the various parts, but it 

 would be wasted labour to enter into minuter detail in a 

 general description, as the form and arrangement of the 

 various parts differ somewhat in the various species, and 

 the minutiae will best be studied by teazing out the parts 

 from the head of whatever larva happens to be available, 

 with needles, under the simple microscope. 



Bespiratory System.-^This is very highly developed in 

 these larvae, and presents many peculiarities which differ 

 widely in the different genera ; and hence the remarks 

 below must be understood to apply to Culex only. The two 

 main longitudinal tracheae are in all, however, of such large 

 size that they may be considered rather as elongated air 

 sacs than as mere tubes for the conveyance of air to the 

 tissues. 



Doubtless they serve a double function ; namely, as 

 receptacles for the storage of air for use during periods of 

 complete immersion, and as hydrostatic organs to secure a 

 proper degree of buoyancy. It is only the two main longi- 

 tudinal trunks that are so largely developed, the remainder 

 of the tracheal system being of no more than the usual 

 complexity in organisms of this sort. Each of these main 

 trunks commences quite abruptly in the prothorax, and, 

 rapidly increasing in diameter, attains its largest dimen- 

 sions in the mesothorax, where, in some species, e.g., in C. 

 nemorosus, there is a marked local dilatation ; in C. pipiens, 

 however, there is no mesothoracic dilatation, and the tube 

 remains of nearly the same diameter throughout the entire 

 length of the abdomen to its termination at the end of the 

 peculiar dorsal process of the eighth segment. The anas- 

 tomoses between the two main stems are trifling, there 

 being only two transverse connections placed in the pro- 

 and mesothorax respectively before the tubes have attained 

 their maximum diameter. The anterior of these two cross- 

 branches is considerably the larger, and immediately in 



