200 PHILIP p. CALVERT. 



surface of the alimentary canal in the head, thorax* and anterior 

 abdomen, posteriorly they become more lateral. In the thorax they 

 lie closely side by side, pass into the head, are connected by a cross 

 trunk at the base of the brain, and then each bifurcates. In the 

 middle of the thorax a cross-trachea connects the two dorsal trunks, 

 and from this cross-trachea a branch is given off to the metastigma 

 of each side. In the thorax each dorsal trunk gives oiF the follow- 

 ing principal branches to its own side of the body : one to the me- 

 sostigma ; one to the third leg ; one which unites with a tracheal 

 coming from the mesostigma, the common trachea running to the 

 second leg; another tracheal runs from the mesostigma to the first 

 leg, but on its way gives off a recurrent which runs forwards and 

 underneath the oesophagus and unites with its fellow of the other 

 side to form a loop, from which loop a branch runs forwards on 

 either side below the oesophagus into the mask. In the abdomen 

 each dorsal trunk is connected by six cross-trachese with the ventral 

 trunk of the same side. The anterior end of each ventral trunk 

 terminates in fine branches in the hind part of the thorax ; between 

 the fifth and sixth of the cross-trachese connecting it with the dorsal 

 trunk the visceral trunk unites with it, the common trunk continuing 

 backwards and finally terminating in tracheoles. Anteriorly, each 

 visceral trunk empties into the branch given off by the dorsal trunk 

 to the second leg, but of the other side of the body. In Aeschna 

 cyanea the visceral trunk unites posteriorly with the ventral trunk, 

 but remains separate in Diplax vulgata and Platetrum depressum. 

 Roster's figure of the tracheal system of Ae. cyanea agrees in the 

 main with the preceding account of Oustalet, except that he shows 

 each ventral trunk to run forwards to the mesostigma of the same 

 side. 



The writer has been able to verify many of the details of distri- 

 bution given by Oustalet, in the nymph of Lestes forcipata. Here 

 the dorsal trunks are six or more times larger in calibre than the 

 visceral or ventral trunks. In the hind part of 9, each dorsal trunk 

 bifurcates, the more lateral branch supplies the lateral caudal tra- 

 cheal-gill, the upper joins its fellow of the other side in the dorsal 

 caudal tracheal-gill. Each visceral trunk empties anteriorly into 

 the branch to the third leg of the other side of the body. 



* Compare the account given of the dorsal trunks for the imago of L. pulchella, 

 p. 179. The significance of this difference is unknown. 



