IX] THE RESPIRATORY SYSTEM 175 



visceral and ventral trunks, and then runs backwards to supply 

 the sides of the ninth and tenth segments, and, in Zygoptera, the 

 lateral caudal gill. The tracheae developed in connection with 

 the branchial basket in Anisoptera are dealt with in the next 

 section. The visceral and ventral trunks unite in segment 7 ; 

 from their junction a short branch runs to the dorsal trunk; 

 a longer branch runs backwards through segments 8-9. The 

 visceral trunks are very poorly developed in Zygoptera. 



The abdominal spiracles are small and non-functional. The 

 branches connecting them with the ventral trunks are short and 

 thin. They appear to be solid except just before and after ecdysis, 

 when the endotrachea is withdrawn through the temporarily 

 open spiracle. The visceral trunks are shining white in colour; 

 they cross one another at the visceral crossing ( Vc) as in the imago. 

 Each ends up anteriorly on the second pedal trunk of the opposite 

 side, close under the dorsal trunk. 



Modifications in the Thorax. In the larval thorax, the dorsal 

 trunks do not bend ventrally downwards, but pass forward in 

 the synthorax dorsally, close under the pleural ridges. Each gives 

 off two alar trunks, which enter the wings at the anal end of the 

 base, forming a loop from which the wing-tracheae arise, and 

 leaving it by the costal side. The alar trunk of the hind-wing 

 then curves downwards, externally to the dorsal trunk, and finally 

 enters the third pedal trachea close to the region of the metastigma. 

 The alar trunk of the fore-wing follows a similar course, ending up 

 on the second pedal trachea. Just in front of the level of this 

 latter trachea, the two dorsal trunks converge closely, and become 

 united by a short thick thoracic anastomosis (TA), from which 

 small branches pass back to the metastigmata. On reaching the 

 level of the mesostigma, each dorsal trunk opens into a kind of 

 chamber below that organ, formed by enlargement of a short 

 cross-branch. In front of this, each dorsal trachea divides into 

 two branches, which pass forwards to the head. In the Zygoptera, 

 the second pedal trachea joins the dorsal trunk just under the 

 mesostigma. 



A peculiar formation connecting the anterior and posterior 

 portions of the dorsal trunk, just in front of and behind the 

 mesostigmatic chamber respectively, is the visceral remnant (figs. 



