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Psyche 3:375-377, 1880.

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PSYCHE.
PNEUMATIC FUNCTIONS OF INSECTS.
BY GEORGE MACLOSKIE, PEINCBTON, N- J.
When handling the larva of a dragon-
The pneumatic function here observed
fly (Libellula) which had lain in a so-
is like that which I have formerly described lution of caustic potash, I found that
in the house-fly,' and which has been since squeezing the thorax protruded the pro-
confirmed by Dimmock.' Other instances
boscis. On removing the pressure, the- of the same class have since come to our 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 a 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 R6au- mur, nor Leon 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.
knowledge.
Gegenbaur ascribes to the abdomen of
these larvae a " branchial movement con- curring with a natatory rn~vement."~
Packard speaks of a "hydrostatic" function in the larva of C~rydalis.~ Reaumur
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 objccts he had ever observed, giving a good account of <he mechanism for working them,5 but he stopped short of what, seems to me the most interesting part.
In the 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. Katuralist, March 1880, v. 14, p. 167. 2 The anatomy of the mouth-parts . . . of some diptera.
Dissertation , . . Leipzig University.
Boston, Williams, 1881.
3 Manuel d'anat. cornpar&, Paris, 1874, 3 138. 4 Amer. naturalist, Sept. 1874, T. 8, p. 533. 6 Ann. dcs sci. nat.,zool., 1852, v. 17, p. 65-100.



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. PSYCHE.
adjoin the ventral nerve-cord.
The large
of filaments which crowd the branchial
pair (which we may call the pneumatic
leaflets.
This action may be aided by
tracheal trunks) suddenly gives out a pressure in the front part of the body which crowd of branches in the abdomen, which drives the air to the rear ; and the paw- subdivide again and again, bretfldng up
matic pressure in the tracheae swells the into a spray of fine filaments which supply delicate filaments and the enclosing bran- the branchial organs.
chial leaflets simultaneonsly with the in- The branchiae consist of a dozen longi-
coming tide of water. The fine membrane
tudiaal columns bound the rectum, each permits the passage of gasea, but not of the bearing about thirty-five pairs of oval water. The contraction of the abdominal branchial leaflets, pilrofttely arranged and 'muscles by reducing the vacuum expels imbricating over each other. Each leaflet both air and water from the branchial receives about two hundred very delicate region, driving the air forward to the tra- filaments from the tracheal branchlete ; the ched system. In a specimen imprisoned
filaments are attenuated towards their ex- with water in a glass tube we found that tremity and end caecally in the sac-like four air-bubbles were expelled with the leaflet,
"Dufour found (in Aeschna) that outgoing tide of water in as many minutes the leaflets are enclosed in pockets or invo- (a result of excitement). Thus the me-
lutions of the intestinal wall ; in Libellah ,chanical principle is nearly the same as in they seem to lie loosely in the rectal cavity.' lung-respiration. The simultaneous inflow The larva respires by drawing in through of air and of a fluid follows the expansion the anus a gentle flow of water, which it of the body-wall, and the contraction of the then expels with force, driving the exhaus- wail induces a reciprocal outflow. lu the
ted water and contained impurities to a safe insect the fluid comes from without, the air dist+mce.
The inflow and outflow may from within;
in the air-breathing verb
occur about fifty times per minute ;
and brate the air comes from without, and the occaaionaily the process will atop for a fluid (blood) from the system, being aided while, especially when the larva is at rest. in its progress by the hearL6 Cutting
There are sphincter valves? at the anus and through the aMominal wall of the larva
muscles for Yegulat-ing the opening and has the same effect as piercing the human closing of the anal lobes and armature, pleura, causing the respiratory organs to and a gangliodc enlargement to supply
collapse and stopping their function. If we this.
But there are no large muscles about prevent the expansion of the abdomen the branchiae and no large ganglia in the of the larva, breathing is temporarily abdomen to suggest special muscular action. arrested. The muscles which line the abdominal wall M, Jnu~set rip BoIlaame7 diacnverod that replate the respiration.
By relaxing they the larval dragon-fly swells out into its permit the abdomen to expand, causing a adult form by a process which is a kind vmuum ' then the wakx
gen-
8 Jb&da Physidogy, 18813, 4th edit., book 2, tly in, and the air fiowa from the pneumatic chap. 2,s 7.
*heal trunks into the many thousands 7 Harper's Annual rec. of sci. . . . 1878, p, 447.



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PS YCffE. 377
of pneumatic efflation. The pressure of
and the adult, a histolysisor disintegration air from within gives definite form to the of the tissues, which must make a new de- body ; puffs up the forehead into soft blad- parture in order to continue their growth, dm-like bumps, and swells out, the wings Balfour suggests thai, instead of a complete like soap-bubbles, until the two sides come break, we may have here only a skipping together and harden into the fine wing- of iutermediate stages. The rule of em-
membrane with its double plate and en- bryo-life is that when a part has a long closed tracheae. This shows the insect's journey before it to reach high organ- wing to be merely an outgrowth (exodeme) ization, it starts early, takes all short cuts, of its body-wall like the pleura of a lob- wad does not delay at the "way-~tations!' ater.
My own observations point to the conclu- The scale-like larva of the beetle Pseph- sion that the fine chitinous frame-work and enus (once described as a cruata<ieati, ledges of the introverted head of the larval Fluviwia) which abounds on the loose fly fairly forecast the characteristic struc- rocks in our streams, has brush-like tra- turcs of the adult, and that the plates of ched filaments (external to its abdomen) the baai-proboscis occupy in the larva the which sweep the .water of its oxygen, and normal place of an endocranium (with
may be observed swelling out and "kick-
which I deem them homolog~us).~ Weis-
ing" at every pulsation ; a result of pneu- mann states that he was unable to trace
matic pressure within the body. the development of these parts, because Reaurnur observed that young fiea can the head was invisible ; and hence he could at will inflate a sac on their foreheads, not work out their homologies.
expanding and contracting it. Weismann,
He found, however, that the head came
in his study of the embryology of diptera, forth to view again from its introverted made an observation which seem to me to position by the influence of mechanical belong to the same category .a The jaws pressure. The abdomen contracts, and of diptera arise far back in the body, pro- this drives the contents of the body for- jecting like limbs, before the true limbs wards so as to eject the head. He specifies
show themselves.
Subsequently the jaws only the fluid contents ; but whatever ope+ travel headwards, become directed for- atesonthem must a fortwri set inmotion the wards instead of transversely, and sink pneumatic dynamics of the tracheae which out of sight within the oral cavity which are then distended with air and largely
+ is now formed by invagination. Then the developed towards the head. Hence the head itself is swallowed up in the trunk, whole head is, is the first instance, driven being lost to view, and thus we have the out by the same aerial impulse which
well-known headless maggot of these in-
subsequently inflates the frontal sac and ,
sects. In the subsequent growth of the propels the proboscis. head-parts this author thinks that there is The same authority states that the fine
a complete discontinuity between the larva branches of tracheae in the system tenni- nate in apindle-cells with thin elastic
a Zeitechr, f. wiss, Zool., 1883, 1W4 and 1866; hd. 13, 14 and 16.
@ Amer. naturalist, March 1880, T. 14, p. 160.



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PS YCHE.
intima. Is it not possible that tracheal pressure may distend these cells like blad- ders, and thus facilitate the aeration of the tissues ? The conditions for their disten- tion seem to be present at every pulsation, though under dissection they are always
collapsed. I have found such terminal
enlargements of the tracheae numerously
developed in the disti-proboscis of the
house-fly. On one occasion I got a fly
in a live-cage with the tip of its pro-
boscis pressing the cover-glass ; and by focussing the microscope on this, I found that with every pulsation there was a cir- cle of flashing lights along the margin
of the proboscis, as if air was rhythmi- cally injected into such sacs. It is easy to understand' how such distension would , promote the function of the tracheae as
carriers of gases between the tissues and the outer world.
Princeton, 24 Nov. 1882.
CLUSTER-FLIES .
BY BENJAMIN PICKMAN MANN, WASHINGTON, D. C. At a meeting of the Biological society
of Washington, held 13 Oct. 1882, Mr.
W: H. Dall exhibited specimens of flies
which had been sent him from New York
state with an account of their habit of con- gregating in large numbers in unused apart- ments of houses, under table-cloths, in pil- low-cases, and wherever similar snug places of concealment could be found. These flies were found from late fall until late spring in such situations, but during the summer they disappeared. Specimens were put into the hands of Dr. C: V. Riley, who made a communication upon them at the meeting
of the same society, 10 Nov. 1882, dwel- ling upon the difficulty of identifying the species of the fly and stating that it was the Pollenia rztdis, described by T. W : Harris as Miisca familiaris, and making
further remarks upon the synonymy. At
this meetirg&Mr. Dall read a letter, received since the presentation of his first coinmu- nication, from the parties who had sent the specimens, giving a highly colored account of the actions of the flies. Dr. Frank
Baker made a more rational statement in
regard to the occurrence of flies in Maine, which were probably of the same species, and had similar habits. Dr. Baker stated that as many of the people in Maine still kept up the custom of the home-production of yarns and spun goods, and these goods, of loose texture, retained upon them a
considerable quantity of their natural
grease, the flies were in the habit of bur- rowing into such goods, to feed on the
grease, and were supposed to cut the fibres. Dr. Riley did not seem to credit the flies with tins habit, but there seems to be no reason to doubt the possibility of such iu- jury, and not much improbability about it. The flies were stated to attach themselves sometimes in clusters suspended from ceil- ings and other supports, and were on this account called ' bcluster-flies." Mr. Dall's informant stated that the flies were proof, at least to a great extent, against the infln- ence of pyrethrum powder, but Dr. Baker
said that if the powder was diffused in an apartment, and the flies were then caused to bestir themselves, and to fly about, they succumbed to the influence of the powder as readily as other flies. Such a difference in observations is not surprising, for it may



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