Biorhiza Group. 139 



are generally found empty, or containing only a little 

 transparent liquid. By chance there may be found, 

 mingled with this liquid, a little piece of the gall which 

 has been swallowed in gnawing a way out. The whole 

 intestinal tract is short and simple, and the Malpighian 

 vessels are particularly small, few in number, colourless, 

 and transparent. In gall-flies just emerging, we find in 

 the last portion of the intestine the excrementitious pro- 

 ducts accumulated during the larval period, and these 

 are discharged soon after the flies take wing ; the 

 quantity is greater in winter generations which pass 

 through a long larval stage. These excreta are always 

 liquid and transparent, and it may not be out of place 

 here to observe, that there is an arrangement by which 

 regurgitation into the anterior portion of the intestine 

 and stomach is rendered impossible. In the great 

 intestine of insects we find certain ridges, the so-called 

 rectal glands, the use of which, according to Leydig, is 

 enigmatical. 



These longitudinal ridges often differ greatly in form 

 and number, but are always found in the same situation, 

 just at the entrance of the great intestine. Leydig 

 expresses a doubt as to their glandular nature, because 

 the essential conditions of a gland are wanting, that is 

 to say, the presence of a secreting epithelium, and the 

 possession of a duct. He considered them rather as 

 respiratory organs, since there are, notably in the larva 

 of the Libellulidae, rectal gills which aid in respiration. 

 The organs were studied and described afresh by Chun \ 



^ C. Chun, Rectaldnisen der Insekien. Verhandlungen d. Sencken- 

 berg. Gesellsch. vol. x. Frankfurt a. M. 1875. 



