38 On the Uses of the Dorsal Vessel. [Juny, 
where they spread themselves in the first pair of legs without send- 
ing out many branches. Always placed at a small distance from the 
dorsal vessel, they pass into the thorax; where, however, they 
separate a little from that vessel, forming round it a kind of S. 
These trachez send branches into the two last pair of legs, in which 
they donot ramify much. When they come into the abdomen they 
approach the dorsal vessel, sending it small ramifications, as they 
do during their whole passage. ‘These ramifications appear to com- 
pose the first membrane of this vessel. ‘These trachez extend to 
the extremity of the abdomen, forming from ring to ring semi- 
circles more or less near each other. Such is the general distribu- 
tion of the trachez in these two genera, in which these vessels have 
a very small diameter. 
The disposition of these two orders of trachez is not quite the 
same in the achetes as in the genera of which we have spoken, 
They have likewise a greater diameter, so that they are more easily 
followed. 
The arterial tracheze begin below the cerebrum, from which, as 
from a central point, they send branches to different parts of the 
head. These branches have no# an equal diameter; and those 
which go to the muscles of the mandibles are remarkably large. 
These branches, penetrating into the mandibles, give numerous 
ramifications, the smallest divisions of which penetrate as far as the 
teeth of thése parts. The arterial trachez furnish equally branches 
to the different parts of the mouth, and extend by two principal 
trunks into the corcelet passing through the opening of the foramen 
occipitale. They then go towards the fore part, along the sides of 
the corcelet, and give pretty numerous ramifications to the rotatory 
muscles of the head, and to the muscles belonging to the corcelet, 
and likewise to those of the legs. Come to the base of the corcelet, 
the arterial trachez form a very large trachea, which passes into an 
opening situated on the lateral and inferior side ; and in this manner 
they receive directly the impression of the external air. This 
trachea then extends to the extremity of the first pair of legs, with- 
out giving out many ramifications. The arterial trachez then pro- 
ceed to the thorax, being always situated at the side of the body. 
They send numerous branches to the muscles of the thorax, prin- 
cipally to those of the wings, the elytres, and legs. “These trache 
furnish likewise branches to the last pair of legs, and to the pul- 
monary trachew, to which they carry air. After having furnished 
these principal branches, and a great number of others much more 
small, the arterial trachee proceed to the abdomen, where they 
form a more complicated apparatus. Extending always along the 
sides of that part, their tranks open into the stigmata by a ramifi- 
cation whose diameter is not so considerable. ‘These trachee 
towards their inside give out six principal branches, divided each 
into two ramifications, much larger, which unite in a single trunk 
that passes into the pulmonary trachee. But before uniting in a 
¢ommon irunk, the large ramifications give out two Jateral branches, 
