180 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
that the powers of the locust as an aeronaut are as great or greater than 
in any other kind of insect. 
That the use of the air-sacs is to buoy up the insect in the air, and 
that by filling and partially emptying the sacs during the process of 
breathing the insect can enlarge its bulk and change its specific grav- 
ity at will, so as to render itself capable of supporting itself on the wing 
with little effort, was first discovered by Sir John Hunter. Newport, in 
his treatise on insects, remarks : 
That this is tho use of the sacs may be inferred from their non-existence in the 
larva state, or in insects that constantly reside on tho ground, more particularly in 
creeping insects ; and it seems further confirmed by the fact that among volant in- 
sects those have tho largest and greatest number of vesicles which sustain the 
longest and most powerful (light. Thus the vesicles are found most developed in 
tho nymt'noptcra, Lcpidoptera Diptera, and some C'oleoptera, and Tlemiptera, in all 
which, in the larva state, there is not the slightest trace of them. A still further 
proof that they are for lightening the body is found in Lucanus cervua. In the male 
of this insect tho largo and heavy mandibles and head, but more especially the man- 
dibles, are not tilled with solid musclo, as in tho Hydrous and others in which these 
parts are more in proportion to the size of other parts of the body, but with an im- 
mense number of vesicles, which in the mandibles are developed in the greatest 
abundance in sacs from long trachea?, that are extended from one end of the organ 
to tho other, so that the interior is almost entirely filled with vesicles. By this beau- 
tiful provision these projecting and apparently unwieldy structures arc rendered ex- 
ceedingly light, while their solid interior fits them for all the purposes of strength 
required by the insect. The largo and apparently heavy body of the humble-bee is 
lightened in a similar manner. In this insect and others of t he same order the vesi- 
cles are fewer, but very much larger than in Colcoptera. The lateral trachea? in the 
abdomen form one continuous chain of dilatations, which are larger in the males of 
the species than in the females. 820 
Also, in his article " on the formation and use of the air-sacs and di- 
lated tracheae in insects," 221 Newport gives further information regard- 
ing the presence of these sacs in other insects : 
In the most active Neuroptera the sacs are very numerous and capacious, especially 
in the dragon-flies, but they are much smaller and fewer in number in the Ephemera, 
the Sialidce, and the scorpion-flies. In the Coleoptera the sacs exist only in the volant 
species, and are more or less numerous and capacious in these in proportion to the 
bulkiness of tho insect and its degree of activity on the wing. This difference exists 
not only in different genera, but in different species of the same genus, according as 
they are winged or apterous species. Thus distinct vesicles are found in the winged 
Carabidce, but not in the apterous, in which the respiratory organs are simply tracheal. 
In the more heavy-bodied genera the vesicles are not confined to the abdominal and 
thoracic regions, but are sometimes extended into other parts, as in the unwieldy 
stag-beetles, in which they are extremely numerous, and occupy the chief portion of 
the interior of the mandibles. In the lcpidoptera, as in the Xeuroptera, they are 
largest in the swiftest and most powerful species, and more especially so in those in 
the males, which are known to be most active on the wing. On the contrary, in tho 
majority of the Orthoptera, which are merely saltatorial in their habits, the trachea 
never assume the form of distinct vesicles, excepting in a few genera, which have the 
power of flight. They retain the arborescent form in the perfect as in the larva state, 
but are considerably enlarged throughout the greater part of their course, their ex- 
220 Todd's Cyclopaedia of Anatomy and Physiology. Article, Insecta. 
221 Transactions of the LinnaBan Society of London, 1851, voL xx, p. 419-423. 
