INTERNAL ANATOMY OF INSECTS. 65 
than we may readily conceive to be necessary for com- 
municating with so many different parts. For, like the 
arterial and venous trees, which convey and return the 
blood to and from every part of the body in vertebrate 
animals, the bronchie are not only carried along the in- 
testines and spinal marrow, each ganglion of which they 
penetrate and fill, but they are distributed also to the 
skin and every organ of the body, entering and travers- 
ing the legs and wings, the eyes, antennee, and palpi, and 
accompanying the most minute nerves through their 
whole course. How essential to the existence of the 
animal must the element be that is thus anxiously con- 
veyed by a thousand channels, so exquisitely formed, to 
every minute part and portion of it! Upon considering 
this wonderful apparatus we may well exclaim, This hath 
Gop wrought, and this is the work of his hands. 
Though in general there is only a pazr of trachee, yet 
in some larvee a larger number have been discovered. 
In those of the Libelluline there are siz. According to 
M. Cuvier, Reaumur, who mentions only four, overlooked 
the two lateral ones that are connected with the spira- 
cles?. The reason of this and other parts of their in- 
ternal structure I shall explain under the next head. 
In the grub of the gad-flies of the horse (str gastri- 
cole Clark), Mr. B. Clark discovered ezght longitudinal 
trachee,—six arranged in a circle and ¢wo minute ones, 
which appeared to him to terminate in a pair of exter- 
nal nipples (spiracles) in the neck of the animal”. This 
4 N. Dict. d’ Hist. Nat. xvii. 541. Reaum. vi. 397. Prate XXIX, 
Fic. 8. shows three of them at a. 
» Essay on the Bots, Sc. 23. t. i. f. 7, 32, &c. 
VOL. IV. F 
