THE HOMOLOGIES OF THE TRACHEAL BRANCHES 

 IN THE RESPIRATORY SYSTEM OF INSECTS 



CLARENCE HAMILTON KENNEDY 

 Department of Zoology and Entomology, Ohio State University 



The following study of the tracheation of the Zygoptera 

 was undertaken to determine the homologies of the tracheal 

 branches that supply parts of the genitalia of the second and 

 third segments of the male. This full investigation will eventu- 

 ally appear in one of the government publications but the study 

 brought to light points of so much greater importance that a 

 discussion of these was given at the Toronto Meetings of which 

 this article is the outline. 



Grassi* has shown the probability that the insect tracheal 

 system was originally a series of disconnected segmental sys- 

 tems which later fused into a connected whole. 



Chapmanf has homologized the main thoracic tracheae 

 which form the main air supply of the wings in the various 

 orders of insects, and has shown us that the tracheal system 

 can be homologized but so far no attempt has been made to 

 refer these back to the more generalized (?) plan found in the 

 tracheation of the abdominal segments. In the majority of the 

 general morphological works on insects the tracheal system is 

 described as being composed of certain longitudinal trunks 

 with various accessory parts in the way of spiracles, air sacs, 

 cross-connections, etc. This is true, but these are not descrip- 

 tions which take into consideration the origin and homologies 

 of the individual parts of the tracheal system. 



The Zygopterous naiad, among the nymphs, of all winged 

 insects, appears to have the abdominal segments least modified 

 from a probable primitive condition. Its abdomen is clyindrical, 

 therefore no parts are displaced or lost by depression. Its gills 

 are at the apex of the abdomen, therefore their position does 

 not modify any but the caudal parts of the system. The abdo- 

 men is elongate so that each segment can be studied individually. 



* Atti dell' Accad. Groenia d. Sci. Nat. Catania (3) T. XIX. 1885. 

 t In "Wings of Insects," Comstock, pp. 27-51. 



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