THE LAETAL GILLS OF THE ODOITATA. 413 



The Larval Gills o£ the Odonata. By G. Gilson, Professor, and 

 J. Sadones, Assistant, at the Zoological Institute of the 

 University of Louvain. (Communicated by Prof. G. B. 

 Howes, Sec. Linn. Soc.) 



[Bead 6th March, 1896.] 



The rectal gills of Lihellula and ^schna are v^'ell known to every 

 student of comparative anatomy, and have attracted much atten- 

 tion since they were first discovered by Swammerdam. Chun's 

 paper on the so-called "rectal glands " of Insects* is usually 

 quoted, as the most complete account of their structure. The 

 works of our predecessors, however, have left room for new 

 researches, and certain important physiological considerations 

 remain unnoticed. 



"Wherever the respiratory organs of terrestrial Arthropods con- 

 sist of numerous lamellse enclosed in a recess or cavity, there is 

 some structure present to prevent their adhering to one another, 

 some provision for keeping open the spaces between these 

 lamellse, and allowing the air, or water, fco freely bathe their 

 surfaces. In the so-called lungs of spiders and scorpions, for 

 instance, the lamellae bear on one face at least numerous chitinous 

 rods or ramified arborescent prominences t. We were, therefore, 

 surprised not to find in the works of our predecessors any mention 

 of the existence of such an apparently necessary mechanism in 

 the Odonata. "We soon discovered, however, that the gills of 

 these insects are no exception to the rule. In Lihellula depressa 

 each lamella bears three conical pillars, two on one face and one 

 on the other (fig. 1). The use of these pillars is obviously the 

 same as that of the prominences of the Arachnidan lung; but, 

 while the latter are only cuticular and merely more or less 

 complex thickenings of that layer, the pillars of Odonata are 

 outgrowths of the cuticle, followed by the subcuticular layer 

 and containing several nuclei. 



The gill of Lihellula and ^schna is a leaf-like folding of the 

 proctodaial epithelium and cuticle. The space between the two 

 laminae contains the main tracheal trunks. These divide very 



* Chun, " Ueber den Bau die Entwickelung iind physiologischen Bedeutung 

 der Eectaldriisen bei den Insekten." Abhandl. der Senckenb. naturf. Gesel., 

 10 Bd., 1876. 



t See L. Berteaux, "Le Poumon des Arachnides." ' La Cellule,' torn. v. fasc. 2. 



