INTERNAL ANATOMY OF INSECTS. 91 



system consisting of veins and arteries ; for by the recent 

 discoveries of M. Carus, it has been satisfactorily proved 

 that insects in their preparatory states 5 have an extrcwas- 

 cular circulation, the arterial and venose currents not 

 being confined \>yparietes. The observations upon which 

 M. Cams' hypothesis is founded, were made in the Au- 

 tumn of 1826 ; and an abstract of their results presented 

 to the Union of German Naturalists and Physicians, 

 which then held its meeting at Dresden, many of the 

 members of which, as MM. Oken, Husche, Heyne, 

 Purkinje, Otto, Weber, and Miiller, had ocular proofs 

 of the reality of the phenomena. 



His first observations were made on the larva ofAgrion 

 Puetta, which swims by means of three vertical laminae 

 attached to the tail ; which, when the wings first appear 

 as rudiments, begin to be exsiccated and are finally de- 

 tached. Each of these lamina?, in its natural vertical 

 position, presents an inferior abdominal and a superior 

 dorsal edge, has two tracheae running along its centre 

 with ramifying bronchiae, and consists of granular sub- 

 stance contained between two strata of the external in- 

 teguments. A current of blood-globules enters each 



to gum or varnish. He saw indeed a few globules, which appeared 

 ten times as big as the others, which swam upon the water, but which 

 he did not regard as component parts of the fluid, but as little drops 

 of grease extravasated by dissection. The fluid of the vessel itself 

 easily mixed with water, and appeared to sink in it to the bottom ! . 

 This proves that it is not of a fatty or oleaginous nature. But the 

 strongest objection is stated by M. Carus, who judiciously observes 2 , 

 That it is contradictory to suppose that a canal should absorb or 

 exude fluids by its parietes in a different form. Further experiments 

 however seem necessary to ascertain the nature of the fluid and its 

 object. 



1 Lyonet Anat. 426. 



2 Introd. to Comp. Anat. ii. 277. Engl. Trans. 



