of a Species of Musca. 133 
organ is closed at its two extremities, and one of these is fixed, as in the 
sarcophaga, to the cesophagus of the insect, without penetrating into the 
interior of the digestive canal. This fact alone completely destroys the 
system of M. Straus and the other advocates of circulation. Lyonnet, in 
his posthumous work, has noticed another of the same description. 
On taking a review of the dorsal organ in the various orders of hexapod 
insects, we find in all the following characters: 1st, It is situated in the 
median dorsal line of the body, immediately beneath the teguments ; 
2d, its axis, which is more particularly the heart or the dorsal vessel of 
authors, is a fibro-fleshy simple cord, without divisions, openings, or 
cavities ; 3d, it is fixed and closed at the two extremities ; 4th, its abdo- 
minal portion is furnished at the sides with wings, sometimes membranous, 
cut or entire, or fixed with ligaments (as among the Hemiptera) under the 
form of a narrow linear border, without any means of connection from 
one end to the other; 5th, the most skilful dissections, the most delicate 
injections, have never detected the least vascular ramification in this or- 
gan, and almost all anatomists have admitted this negative fact, which is 
of such high importance in reference to the question of circulation. 
The movements of the dorsal organ, which have been so imprudently 
designated by the names of systole and diastole, and the agents which de- 
termine them, have been the object of my attentive study. They are 
either wanting or very difficult to be determined in many insects. The 
general movements are principally regulated by the ligaments, the muscles 
attached to the skin, the tracheee put in motion by the act of respiration, 
and the fluctuation of the nutritive liquid. Its proper movements, or pul- 
sations (an improper term), depend principally on the contractibility of 
the fibre. These movements are irregular, and Malpighi has even said 
that he has seen them, in the same individual, sometimes directed from 
the anterior part backwards, and at other times from the hinder part for- 
wards ; a grave testimony against a circulating system. 
What adds still further to the numerous proofs of the non-existence of 
a heart and circulating system in insects is, that immediate death does 
not ensue from cutting the supposed heart through the middle, while the 
same operation, performed on the dorsal vessel, the true heart of a pul- 
monary Arachnid, instantly destroys life. 
I conclude from my dissections, experiments, and reasonings, that the 
existence of an aériferous vascular system adapted to convey the pliysio- 
logical benefits of respiration to all the organs and tissues, is incompatible 
with the presence of a circulating humour. I am satisfied that the latter 
does not exist in insects provided with tracheee, and that the organ which 
has been supposed to perform this function is merely rudimentary, bear- 
ing some resemblance to the heart of the Arachnides; in fact an obsolete 
heart, an organ deprived of every well-determined physiological attribute, 
and perhaps a mere elementary tissuc.* 
* From Annales des Sciences Naturelles, tom. xv. p. 5. 
