130 M. Dufour’s Anatomical and Physiological Studies 
larva; but as no posterior stigmata exist, the tracheal artery is closed at 
its hinder extremity, or terminates in a cul-de-sac. At this place there 
is a considerable interlacement of trachese. Numerous transverse branches 
establish a direct communication between the two great canals. The 
amount of respiration, always proportioned to the degree of vital energy, 
causes the necessity for a much more ramified system in the fly than in 
the preceding metamorphoses. The condition of the winged insect like- 
wise requires utricular trachese, which are truly aérostatic, situate chiefly 
at the base of the abdominal cavity, exactly in the centre of the body, 
and designed to diminish the specific gravity as well as to balance the 
insect in its movements through the air. 
Let us now proceed to consider the digestive apparatus in the larva 
which is voracious in its propensities,—in the nymph which does not eat 
at all,—and in the fly which laps or sucks a liquid food. 
The digestive canal of the larva is seven or eight times longer than the 
body, filiform, rolled upen itself in numerous circumyolutions, It com- 
mences in a large buccal expansion, a rigid gizzard, and four ventricular 
bags. These three organs are not to be met with either in the nymph or 
perfect fly. This greater development of the digestive system is a cause 
or a consequence of the voracity and rapid growth of the larva. The sa- 
livary glands consist of two filiform vessels scarcely half the length of the 
body, and united by a salivary epiploon, which I have met with for the 
first time in these insects. ‘There are four hepatic vessels, long, and as 
slender as a thread, yellow or greenish, free at one end, and uniting in 
pairs to a canal cholidoque, where they discharge bile. 
After the transformation of the larva into a nymph, the buccal cavity, 
the gizzard, and ventricular bags have disappeared, and the alimentary 
canal has lost two-thirds of its length. The chylific ventricle, which is 
narrow and oblong, and more ample than in the two other states of the 
insect, has a rudimentary crop at its origin, and a new bag very different 
from that of the larva. It contains a liquid like syrup, and an intra- 
ventricular vesicle, the singular relict of the evolution of the digestive 
canal in the larva, The salivary glands are still those of the latter, but 
their elements shew a dispositidn to separate in order to assume a new 
form. The hepatic vessels, organs of the earliest formation, present no 
difference from those of the larva and the fly. 
The winged insect scems to have resumed the alimentary canal of the 
larva, but without the three crgans at its commencement. ‘The salivary 
glands, which have now entirely changed their primitive form, have taken 
their place ; a bag with a long neck and a bilobed reservoir is now placed 
at the termination of the esophagus, and the intra-ventricular vesicle has 
not left the least trace of its existence. All the successive modifications 
of creations, all the substitutions, and changes offer points of the highest 
interest, and their parallelism throughout the different metamorphoses 
furnishes considerations of great advantage to organogeny. 
The genital apparatus should haye been spoken of in this plaee ; but 
