of Aquatic Respiration in Insects. 113 



I shall enumerate, in the following table, the various modes of 

 respiration and respiratory organs of Insects : — 



ominal f 



laminar. 





setaceous or 

 lamellar. 



^ 



Chapter I. — Aquatic Branchial Respiration. 



§ 1 . External Branchia. — The abdominal and lateral are or- 

 dinarily of the number of seven pairs ; simple filaments in the 

 Sialis ; of variable forms in the different species of Ephemera ; 

 here in rounded laminae, simple or double, appendiculated or 

 not J there in lamellar tufts, simple or multiplied; otherwise 

 in bunches reverted on the back and distichous; tubulous or 

 simple, or compound in the Phryganides, the Nemouri, the Per- 

 lida. All these filaments, these laminae, these lamellae, are en- 

 riched with trachean embroidery which forms aerigenous organs. 



The caudal branchiae are observed in the larvae of the Agrions. 

 They are three oblong laminae, traversed by trachean branches. 



§ 2. Internal Branchiee. — They are peculiar to some larvae of 

 Libellula. Those of the Calopteryx form a valuable type of 

 transition which had not before been observed. It might be 

 imagined, at first sight, that their three caudal laminae were 

 branchiae ; they are only fins or oars. The rectum is here the 

 receptacle of the true branchiae, which consist of three submem- 

 branaceous processes inserted at the internal side of that stercoral 

 pouch. 



The large nymph-larvae of the Libellula and AEshna present 

 the most complicated and most perfect type of rectal branchiae. 



In the long course of my anatomical investigations, I am sur- 

 pi ised that, up to the last few years, I had never introduced the 

 scalpel into the entrails of such interesting larvae, already rendered 

 so distinguished by the researches of Reaumur, Cuvier and Sukow; 

 at having remained so long a stranger to the wonderful texture oif 

 their rectal branchiae, those air-secreting organs. The following 

 is merely an extract of an extensive investigation, which I hope 

 soon to lay before the Academy. 



