390 MORPHOLOGY OF THE ABDOMEN IX THE ODONATA 



The respiratory system has only been touched upon incidentally. 

 It has been considered from several aspects by many other in- 

 vestigators, and what still remains to be done is of such nature as 

 to make it a problem by itself and to pi;eclude iis consideration as a 

 part of a discussion of general comparative anatomy. Some 

 doubt may also be expressed as to its details having a bearing 

 upon our problems of abdominal adaptation. This is very well 

 suggested by Amans (1885) in the introduction to his excellent 

 study of flight. He says: "L'importance de ce systeme (respira- 

 tory) a ete fort contestie, et apres mure reflection j'ai rejete son 

 etude de mon travail. L'appareil respiratoire offre dans la serie 

 animale une tres grande variete, et pas une seule disposition 

 jouant un role mecanique constant." But while there are sug- 

 gestions pointing toward room for doubt in the case of the 

 Odonata, it is impossible to include its investigation in this paper. 



Nothing has been attempted upon the histologj' of the systems 

 described, or upon the anatomy of the circulatory system. 



The Morphology of Odonate Larvae . 

 I. Zygoptera 



Dufour (1852) more than half a century ago figured and de- 

 scribed the alimentary canal and tracheae of the larvae of two 

 European members of the Zygoptera: Calopteryx virgo and Agrion 

 puella. His details are few and his terms now archaic. Little 

 else was done, if we neglect the tracheae, until the appearance of 

 Calvert's papers between 1910 and 1917. While based upon 

 limited material these papers offer a sound basis and a modern 

 terminology for further work. Tillyard's general work (1917) 

 follows the same lines in part. 



Three species have been dissected by the writer: Calopteryx 

 maculata, Hetaerina americana, and Lestes unguiculata. Partial 

 studies were also carried out on Ischnura posita. Due to a large 

 amount of full grown and well preserved material Lestes and 

 Hetaerina have served best for most of the work. Certain speci- 

 mens in the penultimate moult gave excellent results. Most of 

 the dissections were made by incision along the mid-dorsal line, 

 after which the walls were pinned out flat; some were split 

 ventrally and treated in the same way, while others were cut along 

 each side and the dorsum removed. As the muscles especially are 



