410 EMERGKNCE OF DRAGONFLY-LARViE. 



2. This vigorous respiration is necessary in order to effect a 

 quick exchange of the COo in the tracheal system for air derived 

 fi'om the rectal water-supply. 



.'3. Thereafter, for the first two days of larval existence, rectal 

 lespiration is intermittent only. 



4. This indicates that, for the rest of larval life, rectal respira- 

 tion is only accessory, and is regulated by the sum-total of clH- 

 ciency of the other means of respiration used by the larva. 



o. No true rectal ti-acheal gills are developed in young Zygo- 

 pterid larvie, but two latero-ventr-al folds of thickened epithelium 

 are seen to play a prominent part in the rectal movements. No 

 special ti-acheal development can be seen in tliese rectal folds. 



[Printed oft', 8th Septemher. lUlfi.J 



