IX] THE EESPIEATORY SYSTEM 173 



from it. Another small branch joins a branch from the dorsal 

 trunk. Posteriorly the ventral trunk is connected with the dorsal 

 and visceral trunks of the same side, in the manner already 

 described. Each ventral trunk gives off the following branches : 



(i) Eight short branches to the corresponding abdominal 

 spiracles on the same side. 



(ii) Six branches to the dorsal trunk, as already described. 



(iii) Seven branches to the seven abdominal ganglia of the 

 ventral nerve-cord. Each of these runs inwards transversely, close 

 to the corresponding ganglion. It then divides into two strongly 

 diverging branches, of which the posterior is the largest. The 

 anterior runs forwards to supply the nerve-cord; the posterior 

 gives off a branch to the ganglion, and then runs backwards to 

 supply the nerve-cord. The branches are so arranged on either 

 side of the nerve-cord that the latter appears at first sight to be 

 supplied from two continuous longitudinal tracheae. 



(iv) Branches to the gonads. In the male, the testis is 

 supplied by four branches, arising from the ventral trunk in 

 segments 5-8 respectively. In the female, an immense number 

 of branches supply the ovary, particularly the anterior portion. 

 These penetrate the fat-body, and then branch and re-branch in 

 a complicated manner, forming a strong net, in which the ovary 

 and its enveloping fat-sheath are firmly held. 



B. Modifications in the Larva (figs. 76, 77). 



More is known about the tracheal system of the larva than 

 about that of the imago, not only because the broader and 

 shor er abdomen, and the greater thickness of the tracheal trunks, 

 render dissection easier, but also because, just after ecdysis, almost 

 the whole of the tracheal system of the larva can be followed under 

 the microscope. The general plan is evidently the same, the three 

 pairs of longitudinal trunks having the same relative positions, 

 and giving off much the same branches [in, 147]. 



Modifications in the Abdomen. The dorsal trunks are of great 

 thickness, and of a peculiar semi-metallic reddish or coppery 

 colour. They are strongly bent outwards in the region of the 

 mid-gut in segments 3-4. Posteriorly, about the end of segment 7, 



