and internal, I shall make a few further observations upon this
function. We know little more respecting the mode in which insects
_respire_, except that they breathe out the air by the same kind of
organs by which they receive it,--namely, the _spiracles_, or their
representatives. This has been satisfactorily proved by Bonnet, who
showed that the experiments by which Reaumur thought it established
that insects inspire by their spiracles, but expire through the mouth,
anus, or pores of the skin, are founded on an erroneous assumption.
This physiologist, having observed on the surface of submerged insects
numerous bubbles of air, concluded that they had passed through the
above orifices[301]: but Bonnet found by various experiments carefully
conducted, that this appearance was caused by air which adhered to the
skin and its hairs, and that when the access of this was precluded by
carefully moistening the skin with water previously to immersion, this
accumulation of air-bubbles on its surface did not take place[302]. And
in a variety of instances he observed large ones issue from all the
spiracles, especially the anterior ones. These bubbles sometimes were
alternately emitted and absorbed without quitting the spiracle[303],
and at others were darted with force to the surface of the water, where
they appeared to burst with noise[304]. This author is of opinion that
the _first_ and _last_ pair of these organs are of most importance to
respiration[305]. Reaumur subsequently owned that Bonnet's arguments
had shaken his opinion[306]; and some observations of his own, with
respect to the respiration of the _bot_ of the _ox_, go to prove
that expiration and inspiration are not by the _same_ spiracles;
for he found that the air in this animal was _expired_ by the eight
little _lower_ orifices before mentioned[307], from which he clearly
saw the air-bubbles issue--the _upper_ one he conjectures receives
the air[308]. As the only communication that this grub has with the
atmosphere is by its _posterior_ extremity, it follows, reasoning from
analogy, that the anterior respiratory plates of Dipterous larvæ, which
may be regarded as representing the spiracles of the trunk in insects
in general, are destined for the escape of the air, after it has
parted with its oxygen, received by the anal ones[309]. So that there
seems very good ground for M. Chabrier's opinion that _inspiration_ is
ordinarily by the _abdominal_ spiracles, and _expiration_ by those of
the _trunk_ of insects[310]. He seems to have been led to the adoption
of this opinion, not so much by experiments similar to that of Reaumur
just stated, but by observing that in many instances these two sets
of spiracles differ from each other, the latter having a _convex_ and
the former a _concave_ mouth or bed[311]. In some cases, however,--for
instance during flight,--he supposes the spiracles of the trunk may
_receive_ as well as _emit_ the air[312]: he likewise is of opinion,
and it seems not improbable, that by means of these openings in the
trunk, from the rush of the superfluous air through them, insects
produce those sounds for which they are remarkable,--as the humming
of bees and flies. In the former he thinks the sound is produced by
the pneumatic apparatus covered by the ends of the _collar_; while
in the latter he attributes it to the spiracles in the _metathorax_
behind the wings attended by a poiser[313]. I incline, however, to M.
Dufour's opinion[314],--that the vocal spiracles in the _Hymenoptera_,
as well as in the _Diptera_, are those _behind_ the wings. Perhaps
both theories may be right; for if you take any common humble-bee, you
will find that, in the hand, it produces one kind of sound when its
wings are motionless, and another more complex and intense when they
vibrate. In numerous instances, however, there is no very striking
_external_ difference between the spiracles of the _trunk_ and those
of the _abdomen_: this observation applies more particularly to the
caterpillars of _Lepidoptera_; but whether these receive the air by
those of the abdomen, and return it by those of the trunk, has not yet
been ascertained; and indeed, too little is at present known upon the
subject, and too few facts have been collected, to admit of dogmatizing.
The _external signs_ of respiration in insects are not universally
to be discovered. The alternate contraction and expansion of the
abdomen is, however, very visible in some beetles, bees, the larger
dragon-flies, and grasshoppers. In one of the latter, _Acrida
viridissima_, Vauquelin observed that the inspirations were from
fifty to fifty-five times in a minute in atmospheric air, and from
sixty to sixty-five when in oxygen gas[315]. But M. Chabrier has
given the most satisfactory account of these signs: The abdomen,
says he, is the principal organ of inspiration; it can dilate and
contract, lengthen and shorten, elevate and depress itself. In
flight, in elevating its extremity at the same time with the wings,
it contracts itself, pushes the air into the trunk, and diminishes
the weight of the body by the centrifugal ascending force[316].
In the majority of insects perhaps the dilatation of the abdomen
takes place by the recession of the segments from each other by
means of the elastic ligaments that connect them; in others, as the
_Dynastidæ_, _Galeodes_, &c. by the longitudinal folded membrane
that unites the dorsal and ventral segments--in the _Libellulina_
by similar _ventral_ folds; and in _Cimbex_ by membranous pieces in
the first dorsal segment, which De Geer observed was elevated and
depressed at the will of the animal[317].
Air is as essential to insects in their _pupa_ as in their _larva_
or _perfect_ states. Lyonet, however, Musschenbroek, Martinet, and
some other physiologists, have doubted whether _quiescent_ pupæ
breathed[318]; but Reaumur and De Geer seem to have proved that they
do[319]: and if thrown into water, the same proof of respiration,
by the emission and retraction of a bubble of air takes place, as
in the larvæ; and De Geer found that if one be transferred under
water from one spiracle to another, it will be absorbed by it[320].
Indeed, unless these pupæ had breathed, where would have been the
necessity for the spiracles with which all are furnished? It is
remarkable, however, that all these spiracles do not seem of equal
importance in this respect. Reaumur found that if the _posterior_
spiracles only were closed with oil, the insect suffered no injury;
but that if the _anterior_ ones were similarly treated, it infallibly
died[321]. The respiration however of pupæ seems more perfect in
those that have recently assumed that state, than in those that are
more advanced towards the imago; in which at first, from Reaumur's
experiments[322], it appears that the posterior spiracles were
stopped; and in others still older, from Musschenbroek's[323], even
the anterior ones. Those quiescent pupæ that during that state remain
_submerged_, respire air. De Geer has given an interesting record
of this, in the case of _Hydrocampa stratiotata_. This insect spins
a double cocoon, the outer one thin, and the inner one of a close
texture. In the pupa there are three pair of conspicuous spiracles
on the second, third, and fourth segments of the abdomen, which
are placed on cylindrical tubes, and they appear to have no other
air-vessels. The respiratory gills of the larva having vanished,
like some others of the same genus, they know how to surround
themselves with an atmosphere of air in the midst of the water, so
that the interior of their inner cocoon is impervious to the latter
element--how they renew the air has not been ascertained. Though they
respire air, water is equally necessary, for the animal died when
kept out of water[324].
The great majority of insects respire in much the same manner in
all their states, particularly as to their _external_ organs; for
when the larva breathes by the lateral spiracles, the pupa and imago
usually do the same. The converse of this, however, by no means
holds; for it not unfrequently happens that the two latter breathe
by means of lateral spiracles, though they received the air in their
larva state by an apparatus altogether different. Thus the larvæ of
many _Diptera_ breathe by an anal tube, while the pupa and imago
follow the general system. Sometimes a tribe of insects breathe by an
apparatus quite different in all their states, as we have seen to be
the case with the common gnat[325], which has an _anal_ respiratory
_tube_ in its _first_ state, _thoracic_ respiratory _horns_ in its
_second_, and the _ordinary_ lateral _spiracles_ in its _third_.
Changes also take place in their _internal_ organs. In the larvæ the
respiratory apparatus, especially the tracheal tubes, is often much
larger and more ramified than in the imago; and as the former is the
principal _feeding_ state, there seems good ground for Mr. B. Clark's
opinion--that the respiration is intimately connected with the
conversion of the food[326]. In the _imago_, there appears to be more
provision for storing up the air in vesicular reservoirs, than in the
_larva_. Wonderful is the mode in which some of the changes in the
internal structure, which these variations indicate, must necessarily
take place. They are, however, probably not more singular than those
which less obviously occur in the air-vessels of all insects in their
great change out of the larva into the pupa state. But having before
enlarged on this subject, I need not repeat my observations[327].
The access of air is as necessary to insects even in their _egg_
state[328], and in many cases its presence seems provided for with
equal care, by means as beautiful as those Sir H. Davy and Sir
E. Home have shown to occur in the oxygenation of the eggs and
fœtuses of vertebrate animals[329]. It is only necessary to view
the admirable net-work of air-vessels which Swammerdam discovered
spread over the surface of the eggs of the hive-bee while in the
ovaries[330],--a provision which, from analogy, we may conclude
obtains generally; from the importance which nature has attached
to the oxygenation of the germ while in the matrix. And judging
from analogy, we may infer that the access of this element is as
carefully secured after the egg is laid, as before. The eggs of most
insects being of a porous texture, often attached to the leaves
of plants, and some of them embedded in the very substance of a
leaf or twig[331], are in a situation for the abundant absorption
of oxygen: and the pouch of silk in which the eggs of spiders and
_Hydrophili_ are deposited, may probably, from Count Rumford's
experiments, be of utility in the same point of view. In the case
of the _Trichoptera_ and other insects[332] whose eggs are dropped
into the water enveloped in a mass of jelly, this substance perhaps
serves for aërating the included embryo, in the same way with the
jelly surrounding the eggs of the frog, dog-fish, &c. It would be
desirable to ascertain whether the former jelly be of the same nature
as the experiments of Mr. Brande have shown the latter to be[333]. It
is not improbable that the singular rays that terminate the eggs of
_Nepa_[334] may in some way be connected with the aëration of the egg.
To what I have before remarked with regard to the _vital heat_
of insects[335], I may under this head very properly add a few
further observations. I there stated, that the temperature of these
animals is usually that of the medium they inhabit, but that bees,
and perhaps other gregarious ones, furnish an exception to this
rule[336]. A confirmation of this remark is afforded by Inch, a
German writer, who, upon putting a thermometer into a bee-hive
in winter, found it stand 27° higher than in the open air; in an
anthill, he found it 6° or 7° higher; in a vessel containing many
blister-beetles (_Cantharis vesicatoria_,) 4° or 5° higher. A
thermometer, standing in the air at 14° R., put into a glass vessel
with _Acrida viridissima_, in nine minutes rose to 17°, and a similar
result was observed with respect to other insects[337]. Dr. Martine
says that caterpillars have but two degrees of heat above that of
the air they live in[338]. Coleopterous insects are said to move
slowly and with difficulty when the thermometer sinks to 36°, to
become torpid at 34°, and to lose muscular irritability at a lower
degree[339]. I have before observed that some insects will bear to be
frozen into an icicle, and yet survive[340]: they share this power
with reptiles, fishes, and amphibia. But, however small the excess of
it in some insects above that of the medium they inhabit, it proves
that they possess the power of _generating_ heat. Whether, like the
warm-blooded animals, they generally possess that of _resisting_
heat by perspiration, &c. is not so clear. Yet the heat to which
some can bear to be exposed, basking at noon, as Dr. Clarke informs
us[341], on rocky and sandy places, exposed to the full action of
the sun, appears sufficient, if not resisted by some principle of
counteraction, to roast them to a cinder. That bees perspire is well
known, but probably not singly.
When the respiration of insects is suspended by immersion in any
fluid, it is often resumed, even when it has been long and they are
apparently dead, if they be brought into contact with the atmosphere.
Reaumur found this to be the case with bees[342]; and Swammerdam
tells us that the maggot of the cheese-fly (_Tyrophaga Casei_) lived
six or seven days in rain-water[343]: he found it so difficult to
kill the larva of _Stratyomis Chamæleon_, which he first immersed
twenty-four hours in spirits of wine, and then put them several days
in water, without killing them,--that he lost his patience, and
dissected them alive. He tried to drown them also in vinegar, in
which they held out more than two days[344].
That the suspended animation and subsequent death of most terrestrial
insects when thrown into water is caused by the want of _air_, is
evident from this,--that the same effect ensues if the spiracles
be covered with any oily or fatty matter. In this case too, their
vital powers soon become suspended: they revive, if the suffocating
matter be soon removed; and if this be not done, infallibly perish.
This fact was known to the ancients, for Pliny observes that bees
die if dipped in oil or honey[345]. One exception to this law has
been before mentioned[346]: a similar contrivance secures the
cheese-maggot from having its respiration interrupted by its moist
and greasy food; the grub also of _Sarcophaga carnaria_, and of other
_Muscidæ_ probably, has its posterior spiracles placed in a plate
at the bottom of a kind of fleshy pouch, which has the shape of a
hollow, truncated, and reversed cone. This pouch the grub can close
whenever it pleases, so as to cover its spiracles[347]. And numerous
other larvæ, both of _Diptera_ and _Coleoptera_ that devour unclean
and oily food, have doubtless some protection of this kind for their
spiracles and respiratory plates.
I am, &c.
FOOTNOTES:
[144] _Anat. Compar._ iv. 296.
[145] Plin. _Hist. Nat._ _l._ xi. _c._ 3. Even Aristotle seems to
have given into the common opinion. _De Respirat._ _c._ 3, 9. &c.
[146] _Philos. Trans._ v. 2011. Works, 4to. i. 79, 112.
[147] Aristot. _Hist. Animal._ _l._ viii. _c._ 27.
[148] _On Air and Fire_, 148, 155.
[149] _Tracts_, 208.
[150] _Mem. on Respirat._ 75.
[151] _Ann. de Chimie_, xii. 273.
[152] F. L. A. Sorg, _Respirat. Insect. et Verm._ Ellis, _Inquiry
into Chang. prod. on Atmosph. Air by Respirat._ &c. 69.
[153] _Ann. de Chimie_, xii. 273.
[154] Sprengel, _Commentar._ &c. 27--.
[155] PLATE XXIII. FIG. 2. and PLATES VIII. IX. XVI. XXIX.
_c´_,_h´´_, _m´´_, _A´´_, _D´´_.
[156] Moldenhawers (_Anat. der Pflanz._ 314--.) affirms that
the spiracles of most insects are quite closed: but Sprengel
(_Commentar._ § 8.) has satisfactorily refuted that opinion.
[157] PLATE XXIII. FIG. 2.
[158] Sprengel, _Commentar._ § 7.
[159] _Ibid._ _t._ iii. _f._ 30.
[160] PLATE XXIX. FIG. 23.
[161] Ibid. 8.
[162] Sprengel, 7. _t._ iii. _f._ 30.
[163] _Ibid._ _t._ ii. _f._ 22. _t._ iii. _f._ 29.
[164] PLATE XXIX. FIG. 29.
[165] Ibid. FIG. 16. Sprengel, _Ibid._ 9. _t._ 1. _f._ 4-6.
[166] _Ibid._ 9. _t._ i. _f._ 9.
[167] PLATE XXIX. FIG. 16. _a._
[168] Sprengel, _Ibid._ _t._ iii. _f._ 27.
[169] Sprengel, _Commentar._ 7--.
[170] Sprengel, from whom I have borrowed this quotation, expresses
the time by "_scripulo horæ_." This word is of uncertain meaning,
being scarcely ever applied to _time_; but as it means the
twenty-fourth part of an ounce, Faber conjectures it may mean the
same portion of an _hour_.
[171] Sorg, _Disquisit. circa respirat. insect._ 27, 46, 66. Sprengel
_ubi supr._ 11--.
[172] Chabrier _sur le Vol des Ins._ _c._ l. 454.
[173] PLATE XXIX. FIG. 28. _A´´_.
[174] _Ibid._ FIG. 23.
[175] Sepp. I. iv. _t._ ii. _f._ 3.
[176] _Ibid._ _t._ xiv. _f._ 3.
[177] _Ibid._ _t._ v. _f._ 6, 7.
[178] _Ibid._ _t._ i. _f._ 7, 8.
[179] _Ibid._ _t._ x. _f._ 6, 7.
[180] _Ibid._ v. _t._ i. _f._ 3.
[181] _Sphinx Labruscæ_ Merian _Surinam._ 34.
[182] PLATE XXIX. FIG. 28. _A´´_.
[183] Swammerd. _Bibl. Nat._ _t._ xxvii. _f._ 5. Compare Sturm
_Deutsch. Fu._ i. _t._ v. _f._ r.
[184] PLATE XXIX. FIG. 12. _c´_.
[185] De Geer, i. 81. _t._ v. _f._ 10. _f._
[186] _Sur le Vol des Ins._ _c._ i. 459.
[187] Reaum. iv. 246. _t._ xix. _f._ 8. _s._
[188] In this tribe, which I forgot to remark before, (see VOL. III.
p. 549--.) there seems both _prothorax_ and _collar_.
[189] VOL. III. p. 550, 559. &c.
[190] PLATE VIII. FIG. 14. h´´.
[191] PLATE XXIX. FIG. 14, 15. m´´.
[192] Ibid. FIG. 15. a.
[193] Ibid. FIG. 14, 15. b.
[194] Ibid. FIG. 25. _k´´_.
[195] Chabrier _sur le Vol des Ins._ _c._ iii. _t._ vi. _f._ 4. _Sa,
Sp._
[196] PLATE IX. FIG. 21. _m´´_.
[197] PLATE VIII. FIG. 9.
[198] VOL. III. p. 705--.
[199] VOL. III. p. 708.
[200] Sprengel, _Comment._ 3.
[201] _Ibid._
[202] vi. 398.
[203] De Geer, ii. 635.
[204] _Fourmis_, 22.
[205] _Osservaz. &c. sullo Iulus fœtid._ 14--.
[206] They are particularly visible in an undescribed East Indian
species, (_S. alternata_ K. M. S.) with scuta alternately black and
yellow.
[207] PLATE XXIX. FIG. 20. _A´´_.
[208] De Geer, vii. _t._ vi. _f._ 3.
[209] VOL. I. p. 254--.
[210] De Geer vi. 67. _t._ iii. _f._ 10. _ss._ 14. Mr. W. S. MacLeay
(_Philos. Mag. N. Ser._ No. 9. 178.) says that in this grub the
longitudinal trunks of the Tracheæ send off at equal distances
lateral branches just as if there were spiracula to correspond with
them. This is evidently a preparatory step to the formation of those
that ultimately appear in the perfect insect.
[211] De Geer 66. _t._ iii. _f._ 13.
[212] PLATE XIX. FIG. 11. _a._
[213] Reaum. iv. 375--. _t._ xxvi. _f._ 7, 8.
[214] _Ibid._ 555. _t._ xxxv. _f._ 10. _ss._
[215] _Ibid._ 519--. _t._ xxxvii. _f._ 3, 4.
[216] PLATES XVI. FIG. 9. _a b._ XIX. FIG. 9, 10, 12, 13. _a._ XXIX.
FIG. 3-7.
[217] PLATE XIX. FIG. 9. _a._
[218] PLATE XIX. FIG. 9. _b._
[219] Compare Swamm. _Bibl. Nat._ i. 154. _t._ xxxi. _f._ 5. Reaum.
iv. 601--. _t._ xliii. De Geer vi. 317--. _t._ xvii. _f._ 2-8.
[220] Swamm. _Ibid._ _t._ xxxi. _f._ 7, 8.
[221] Reaum. iv. 607.
[222] PLATE XIX. FIG. 12. _a._
[223] Reaum. iv. _t._ xxxii. _f._ 2. _e._
[224] Mr. W. S. MacLeay (_Philos. Mag. N. Ser._ n. 9. 179.) asserts
that what Reaumur (iv. 487. _t._ xxx. _f._ 6. _ll_) calls the first
pair of legs of this grub, are the usual palmated stigmata which
occur on the humerus of the larvæ of _Muscidæ_. It does not appear
whether he has himself examined this grub, but Reaumur (443) states
that it has _seven pairs of legs all armed with claws_. If this is
correct, it is not properly a palmated organ.
[225] Reaum. iv. _t._ xxx. _f._ 10.
[226] Reaum. iv. _t._ xxx. _f._ 447--.
[227] _Ibid._ 456. _t._ xxxi. _f._ 1-7.
[228] PLATE XIX. FIG. 13. _a._
[229] _Bibl. Nat._ ii. 44.
[230] PLATE XIX. FIG. 10. _a._
[231] Reaum. v. _t._ iv. _f._ 6. _s, u._
[232] VOL. II. p. 275--.
[233] De Geer vi. 395--. _t._ xxiv. _f._ 16. 18. _d._
[234] v. _t._ vi. _f._ 1, 2.
[235] De Geer iii. 367. _t._ xviii. _f._ 1, 2, 9.
[236] _Ibid._ vi. 36. 194--. _t._ ii. _f._ 2, 3. _s._
[237] PLATE XVI. FIG. 9. _a. b._
[238] De Geer ii. 539--. _t._ xi. _f._ 12, 16, &c.
[239] De Geer i. 526--. _t._ xxxvii. _f._ 2-6.
[240] _Ibid._ iv. 362--. _t._ xiii. _f._ 16-19.
[241] VOL. I. p. 282--. II. 365--.
[242] See Reaum. vi. _t._ xlii.--xlvi. and PLATE XXIX. FIG. 3-5.
[243] Reaum. _Ibid._ _t._ xlv. _f._ 2.
[244] PLATE XXIX. FIG. 5. De Geer ii. 624--.
[245] Ibid. FIG. 4. De Geer _Ibid._ 647--.
[246] Ibid. FIG. 3. De Geer _Ibid._ 653--.
[247] Ibid. FIG. 6. De Geer _Ibid._ 727--.
[248] Reaum. vi. 465.
[249] _Ibid._ _t._ xlii. _f._ 4, 5. De Geer ii. 623.
[250] _Ibid._ 648. _t._ xvii. _f._ 11, 12.
[251] VOL. III. p. 154. De Geer ii. 697--. _t._ xxi. _f._ 4, 5, 12.
[252] De Geer _Ibid._ 666--. _t._ xix. _f._ 6.
[253] Reaum. vi. 393. _t._ xxxvi. _f._ 8, 9. _t._ t.
[254] Reaum. vi. 395. _t._ xxxvi. _f._ 8-9. _c. c._
[255] PLATE XXIX. FIG. 21.
[256] Marcel de Serres (_Mem. du Mus._ 1819. 137, &c.) calls the
_tubular tracheæ_ that _receive_ the air, _arterial tracheæ_, and the
_vesicular_ ones which act as _reservoirs_, _pulmonary tracheæ_.
[257] PLATE XXIX. FIG. 1. 2.
[258] Treviranus _Arachnid._ 7--. _t._ l. _f._ 1. _r. f._ 10. Comp.
_N. Dict. d'Hist. Nat._ xxx. 419. Latreille calls these gills
_Pneumo-branches_.
[259] Treviranus _Ibid._ 24. PLATE XXIX. FIG. 1.
[260] PLATE XXI. FIG. 3. _a b._
[261] Ibid. _a._
[262] Ibid. _b._
[263] Sprengel _Commentar._ _t._ i. _f._ 1.
[264] _Ibid._ _f._ 10.
[265] _Ibid._ _t._ ii. _f._ 15.
[266] Malpigh. _De Bombyc._ _t._ iii. _f._ 3.
[267] _Ibid._ _t._ iv. _f._ 1.
[268] Lyonet _Anat._ 101.
[269] Lyonet _Anat._ 101.
[270] Sprengel (_ubi. supr._ 16.) says that he never found more than
_two_; but as Lyonet affirms that he has very often separated them
(102), his accuracy cannot be questioned.
[271] Lyonet _Anat._ 103.
[272] _Ibid._ Cuv. _Anat. Comp._ iv. 438. This author says that the
_intermediate_ tunic is the spiral thread (437).
[273] Lyonet 102.
[274] Ibid. 104. Sprengel _Commentar._ 17.
[275] Lyonet 104. Sprengel _Commentar._ 17.
[276] Lyonet 102. Malpigh. _De Bombyc._ 12. Reaum. i. 130.
[277] Swamm. _Bibl. Nat._ _t._ ii. _f._ 7.
[278] Lyonet 411.
[279] Professor Kidd (_Philos. Trans._ 1825. 235.) conjectures that
the tracheæ, as well as air-vessels, may possibly be blood-vessels;
but this hypothesis is inconsistent with the fact recently discovered
by Dr. Carus, of a circulation, by other means, in larvæ. See Carus
_Introd. to Comp. Anat._ &c. ii. 400.
[280] _N. Dict. d'Hist. Nat._ xvii. 541. Reaum. vi. 397. PLATE XXIX.
FIG. 8. shows _three_ of them at _a_.
[281] _Essay on the Bots, &c._ 23. _t._ i. _f._ 7, 32, &c.
[282] _Ibid._ 49. Valisnieri i. 101. _t._ vi. _f._ 4. &c.
[283] _Bibl. Nat._ i. 149. a. _t._ xxix. _f._ _a._ Cuv. _Anat. Comp._
iv. 439. Malpigh. _De Bombyc._ _t._ iii. _f._ 2.
[284] _Sur le Vol des Ins._ c. ii. 336. note 1.
[285] Swamm. _Bibl. Nat._ _t._ xvii. _f._ 9. Cuvier _Ibid._ 440.
[286] PLATE XXIX. FIG. 10. _a._
[287] Ibid. _b._
[288] De Geer vi. 374.
[289] Reaum. v. 40. _t._ vi. _f._ 4, 7.
[290] Sprengel _Comment._ 4.
[291] De Geer ii. 667, 675.
[292] Reaum. vi. 394--.
[293] Reaum. vi. 394--. Cuv. _Anat. Comp._ iv. 440--. _N. Dict.
d'Hist. Nat._ xvii. 540--.
[294] PLATE XXIX. FIG. 9. _a, b._ Reaum. vi. 418--. 450.
[295] Cuv. _Anat. Comp._ iv. 441.
[296] VOL. III. p. 583.
[297] Sprengel _Comment._ 17. _t._ iii. _f._ 24.
[298] _Ibid._ _t._ i. _f._ 11.
[299] _Sur le Vol des Ins._ c. ii. 336. note 1.
[300] Sprengel _Comment._ 13--. These _oscula_ or pores in the straw
of _Triticum hybernum_, as figured by Mr. Bauer's admirable pencil,
(Sir J. Banks _On the Blight, &c._ _t._ ii. _f._ 3.) exactly resemble
the spiracles of insects.
[301] Reaum. i. 136.
[302] Bonnet _Œuvr._ iii. 39--.
[303] _Ibid._ 43.
[304] _Ibid._ 50.
[305] _Ibid._ 69.
[306] De Geer ii. 117.
[307] See above, p. 50.
[308] Reaum. iv. 520.
[309] Mr. B. Clark thinks that he has discovered spiracles in this
larva in the usual situation, (_Essay on the Bots, &c._ 48. _t._
ii. _f._ 3.) but they are probably analogous to the spiraculiform
tubercles of _Œ. Ovis_. Reaum. iv. 566. _t._ xxxv. 17-19. t.
Vallisnieri (_Esperienz. &c._ 136) notices them.
[310] _Sur le Vol des Ins._ c. i. 423.
[311] _Ibid._ 454. and c. iv. 66. note 1.
[312] _Ibid._ c. i. 453.
[313] _Ibid._ 459, 456.
[314] _Ibid._ 459.
[315] _Annal. de Chim._ xii.
[316] _Sur le Vol des Ins._ c. i. 423, 454. c. iii. 344. c. iv. 66.
[317] De Geer ii. 946--.
[318] Lesser, L. i. 124. note *. Lyonet _Anatom._ pref. xii. De Geer
ii. 132.
[319] Reaum. i. 399--. De Geer i. 37--.
[320] _Ibid._ 40.
[321] Reaum. i. 400.
[322] _Ibid._
[323] De Geer ii. 129.
[324] De Geer i. 531--. _t._ xxxvii. _f._ 13. s. Compare Reaum. ii.
396--.
[325] See above, p. 51--.
[326] In _Linn. Trans._ iii. 302.
[327] VOL. III. p. 195--.
[328] Spallanzani found that the eggs of insects placed under the
exhausted receiver of an air-pump, or in any small closed vessels,
did not hatch, though every other condition for their development was
present. _Opusc. de. Phys._ i. 141.
[329] _Philos. Trans._ 1820. 213.
[330] _Bibl. Nat._ i. 204. b. _t._ xix. _f._ 5.
[331] VOL. I. p. 446--. III. p. 76.
[332] Ibid. 68--.
[333] _Philos. Trans._ 1820. 218.
[334] VOL. III. p. 94.
[335] VOL. II. p. 228--.
[336] Ibid. p. 211.
[337] Inch, c. iv. _Ideen zu Einer Zoochemie_, 68--.
[338] _On Thermom._ 141.
[339] Carlisle in _Philos. Trans._ 1805. 25.
[340] VOL. II. p. 229.
[341] _Travels_ ii. 482.
[342] Reaum. v. 540.
[343] Swamm. _Bibl. Nat._ ii. 65. a.
[344] _Ibid._ 48. a.
[345] _Hist. Nat._ _l._ xi. _c._ 19.
[346] Swamm. _Bibl. Nat._ ii. 64. a.
[347] Reaum. iv. 428. _t._ xxix. _f._ 2. _c, s._
LETTER XXXIX.
_INTERNAL ANATOMY AND PHYSIOLOGY
OF INSECTS, CONTINUED._
CIRCULATION.