Sy, CE B.. 
« PNEUMATI€ FUNCTIONS OF INSECTS. 
BY GEORGE MACLOSKIE, PRINCETON, N. J. 
When handling the larva of a dragon- 
fly (Libellula) which had lain in a so- 
lution of caustic potash, I found that 
squeezing the thorax protruded the pro- 
boscis. On removing the pressure, the 
proboscis folded itself by its elasticity, 
and returned to its mask-like condition 
of rest. The experiment could be repeated 
indefinitely, just as we extend and retract 
a pair of lazy-tongs. The muscles having 
been destroyed in these specimens, the 
movements were purely mechanical, de- 
pending on air-pressure and the elasticity 
of the chitinous membranes. In the fresh 
specimens similar pressure of the thorax 
(and in less degree pressure of the abdo- 
men) both protrudes the proboscis and 
swells its base with air. A cushion in the 
flexor-side of the angle of the proboscis is 
much inflated, and on pricking it with a 
needle it collapses and the power of pro- 
trusion is almost destroyed. The proboscis 
has at its tip muscles for abducting and 
adducting the terminal lobes relatively to 
each other; near the base it has h few 
muscles for guiding and aiding its move- 
ments. It is-richly supplied with tracheae, 
and thus is in direct communication with 
the pneumatic system of the head and 
thorax. It is surprising that neither Réau- 
mur, nar Léon Dufour, nor the other in- 
vestigators who made this larva a subject 
of special study, detected its mode of pro- 
truding the proboscis, a matter of easy 
observation. 
in the larva of Corydalis.* 
The pneumatic function here observed 
is like that which I have formerly described 
in the house-fly,’ and which has been since 
confirmed by Dimmock.? Other instances 
of the same class have since come to our 
knowledge. 
Gegenbaur ascribes to the abdomen of 
these larvae a ‘‘ branchial movement con- 
curring with a natatory movement.”? 
Packard speaks of a ‘‘hydrostatic” function 
Réaumur 
watched the backward flow of water from 
the anus of the larvae of libellulids, and 
stated that it aids in propelling the animal 
(a view which has been repeated by others ; 
but the main organs of propulsion are the 
nimble limbs). Dufour admired the struc- 
ture of their pneumatic branchiae as the 
most beautiful objects he had ever observed, 
giving a good account of the mechanism for 
working them,’ but he stopped short of what 
seems to me the most interesting part. 
* Inthe thorax are six tracheal trunks, 
of which the two dorsal ones are exceed- 
ingly large, and with few branches save at 
their anterior and posterior extremities ; 
two others are smaller, line the alimentary 
tract, and supply it with many branches ; 
the remaining two are very small and 
1 Amer. Naturalist, March 1880, v. 14, p. 157. 
2 The anatomy of the mouth-parts . . . of some 
diptera.. Dissertation ... Leipzig University. 
Boston, Williams, 1881. : 
3 Manuel d’anat. comparée, Paris, 1874, § 138. 
4 Amer. naturalist, Sept. 1874, v. 8, p. 533. 
5 Ann. des sci. nat., zool., 1852, v. 17, p. 65-100. 
