1815.] On the Uses of the Dorsal Vessel. Al 
ing and irregular; the external extends in a straight line to the 
opening of the seventh stigma, where it receives the impression of 
the air as well as the internal trunk. These two trunks of pulmo- 
nary tracheze communicate with each other by meanis of the lateral 
branches, which are six in number on each side; but besides these 
Jateral branches, there exists one at the base of the body, which 
unites the two systems of pulmonary trachee. ‘This apparatus, in 
combining with that of the arterial trachez, forms an admirable 
whole, which the silvery colour of the tracheze renders still more 
agreeable to the eye. The internal trunk of the pulmonary trachee 
sends out a great many branches to the dorsal vessel, branches which 
divide themselves to infinity. We see how complicated the pul- 
monary trachee are in this genus, and all in order that there may 
be a greater reservoir of inspired air. . 
The arterial trachee rise in the head below the cerebriform 
ganglion. ‘They give out there large branches, which spread them- 
selves in the muscles of different parts of the mouth. They go 
likewise to the upper part of the head, and unite with the trachez 
that proceed to the eyes. ‘They then pass into the corcelet, always 
along the side of the body. The two great branches parallel to the 
common trunk of the arterial trachez, and which open into the 
tremaer situated at the base of the corcelet, may be considered as 
belonging to this system, though they appear to be divisions of pul- 
monary trachee. ‘The external trunk of the arterial trachee gives 
a great many ramifications to the muscles of the thorax. We have 
not given a figure of them, because we wished to render our repre- 
sentation more intelligible; for if we had exhibited all the ramifi- 
cations that we perceive, it would have been very difficult to have 
followed the direction of the principal trachez ; so that we should 
have run the risk of failing in our object. The arterial trachee 
unite with the pulmonary towards the base of the corcelet. They 
then penetrate into the thorax by three principal branches, and the 
two external unite, forming a kind of oval, before which the inter-. 
mediate branch unites with the first pulmonary trachea, which goes 
to the third pair of legs. ‘These arterial tracheze form soon after 
two principal trunks, situated further down, and more externally, 
than the trunks of the arterial trachee. Each of them sends a 
lateral branch, which opens into the stigmata; so that there exist 12 
lateral branches, since there are six stigmata, and each receives two. 
We may even reckon 14, since the whole of the system terminates 
in the seventh stigma by two principal branches. ‘The trachew 
which go to the organs of generation proceed from the third lateral 
branch: these trachee are very large and numerous. But besides 
these trachew, the common trunks furnish a great number to the 
intestinal viscera. We have not given figures of them, for the 
reason already stated. 
The descriptions which we have given of the various respiratory 
organs in insects, must have shown that by means of this compli- 
cated apparatus there is a real circulation of air in that order of 
