THE ANATOMY OF THE LARVA 



49 



front of it, each trunk splits up into a number of branches, 

 which enter the head and are distributed to the various 

 organs contained in it. The large anterior cross branch 

 gives off no branches, but the hinder one supplies some 

 twigs to the wall of the intestinal canal, and to the hepatic 

 glands. 



In the larvae of A?i. Bossii, however, and presumably of 

 other species of that genus, the communication between the 

 two main trunks is extremely free, as not only are they 

 continued beyond the end of the thoracic dilatation to unite 

 with each other in the middle line in the form of an arch of 

 nearly uniform diameter, but a smaller anterior branch 

 unites with its fellows to form a second concentric arch, of 



Fig. 14. — Larva of Anopheles Bossii, seen from in front, to show the 

 tracheal arches, and their anastomosing loops. 



but little less calibre. Moreover, as will be seen in the 

 figure, each arch gives off eight branches, which anastomose 

 with each other to form a series of loops, four on each side, 

 those of the larger arch being directed tangentially, while 

 those of the smaller run forwards ; so that, in addition to 

 the transverse branches described above, there are no less 

 than four channels of communication between the main 

 trunks of opposite sides. 



From each of the main trunks in the thorax there 

 issue also three rather large branches, one for each seg- 

 4 



