Jan., 1922 the tracheal branches of insects 87 



thorax have moved dorsad and those of the mesothorax and 

 metathorax have begun to take on the place and shape of wing 

 pads. The simple pleural trachea, pt, tracheates them in the 

 beginning and follows them as they pass from the lateral to 

 their final dorsal position. The pleural trachea is the anterior 

 or costal wing supply and is the original wing supply as this 

 devlopment shows. As the wing folds (later, pads) pass dorsad 

 they pass the tips of an anterior and di posterior dorsal connectives 

 in each segment and take on connections with these. Also the 

 anal apex of each wing trachea {pleural trachea) connects also 

 with the anterior latero-tergdl trachea of the succeeding segment. 

 Thus each wing in Lestes has four tracheal connections. 



Several puzzling shifts and specializations have taken place. 

 In segment 1 the leg branch is lost and the anterior spiracular 

 connective has shifted from the spiracle down onto the gangli- 

 onic trachea. This has occurred also in the second and third 

 thoracic segments so that the posterior latero-tergal trachea in 

 each case has shifted to arise from near the spiracle. 



In the metathorax the metathoracic tip of the posterior dorsal 

 connective has shifted down onto the vertical spiracular trunk. 

 This conclusion is arrived at by elimination of the other tips. 

 This solution homologizes the tracheation of the hind wing with 

 the tracheation of the front wing. 



In the thorax the ganglionic trachea have shifted down onto 

 the leg trachea in each segment, and in each segment a second 

 or accessory ganglionic trachea, agt, has appeared. 



The shortening of the spiracular trunk in the mesothorax 

 has pulled the leg trachea of the prothorax out of shape and has 

 greatly shortened the anterior spiracular connective of the 

 mesothoracic spiracle so that the lateral trunk becomes a 

 second dorsal trunk in the insect's neck. 



This work in tracheation is very much confused by mal- 

 formations and adventitious branches. Frequently there are 

 two or even three anterior or posterior latero-tergal trachece, 

 sometimes two pleural trachece, etc. One has to examine enough 

 specimens that these abnormalities are recognized as such and 

 no longer confuse. This readiness of the tracheal system to 

 develop new branches has been one of the things which has 

 made homologization of the branches seem a hopeless task. 



The tracheation of the internal organs seems to be largely 

 fortuitous except for two large trachea that run from the 



