94 Bulletin of the Brooklyn Entomological Society Vol. XV 



not simple and numerous loops in lamellar form as in the Ani- 

 soptera, but a fairly elaborate series of anastomosing loops. 



The difference between Anisoptera and Zygoptera is then that 

 in the latter the oxygen must pass through a thick outer cuticle, 

 the cellular hypodermis beneath, then to be taken up the tracheal 

 capillaries which lie in the alveolar meshwork. It will be seen 

 at once that the Anisopteran system is highly specialized com- 

 pared to that of the Zygoptera. In the Zygoptera, however, the 

 .capillarization of the caudal gills appears to be not the only 

 source of oxygenation. In experimenting on the necessity of the 

 caudal gills to the life of damselfly larvae I removed the caudal 

 gills (there is a special breaking point at the base of each gill) 

 in successive instars ; while there was regeneration following each 

 amputation, this took place only during ecdysis, and the newly 

 formed gills were at once removed. The presence of a breaking 

 joint in itself indicates that the organism can exist without the 

 caudal gills, while the very copious sternal capillarization of the 

 abdominal segments may be quite efficient in supplying the re- 

 spiratory wants of the animal in the absence of the gills. 



Among insects the respiration of Anisopteran Odonata is 

 unique; and while the principles derived from its study apply 

 generally, yet the strutcures of other insects are rather more like 

 those of Zygoptera. Thus, may-flies and stone-flies have both 

 lateral and caudal gills with a tracheal capillarization much like 

 that of the Zygoptera. There is also the point that in aquatic 

 insects so much of the structure cannot be understood unless one 

 enters into a discussion of the phylogeny. For this there is no 

 place in this paper. Yet the following may be noted: We have 

 what we may call primarily amphibious groups such as stone- 

 flies, may-flies and Odonata, and secondarily amphibious groups 

 which include other aquatic forms. That is, the first have re- 

 tained their original amphibious habits as indicated by fossils 

 back to carboniferous times, while the others became terrestrial 

 and then secondarily aquatic. Among the latter are to be in- 

 cluded the Trichoptera, Coleoptera, Diptera, and Hemiptera. 



Fixation Method. — Another method of internal oxygenation is 

 that of fixation of oxygen by some carrier in the blood. In a 

 few rare cases the carrier is colored. Thus, in some species of 



