INTERNAL ANATOMY OF INSECTS. 91 
system consisting of veins . d arteries ; for by the recent 
discoveries of M. Carus, it has been satisfactorily proved 
that insects in their preparatory states, have an extravas- 
cular circulation, the arterial and venose currents not 
being confined by parietes. 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 Midler, had ocular proofs 
of the reality of the phenomena. 
His first observations were made on the larva of Aerion 
o 
Ptiella, 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 laminae, in its natural vertical 
position, presents an inferior abdominal and a superior 
dorsal edge, has two tracheae running along its centre 
with ramifying bronchia?, 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 *, 
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—. 
8 Introd. to Comp. Anal, ii, ?77- Engl. Trans. 
