_Scolechiasis_; with this difference however, that _Acari_ most
commonly take their station upon them in their _perfect_ state. You
have doubtless often observed the common dung-beetles (_Geotrupes_)
covered on the underside of their body with small mites (_Gamasus
Coleoptratorum_) which look as if they were engaged in suction--they
are often so numerous that no part is uncovered; they also attack
other beetles[1006], and are sometimes found on humble-bees. They are
easily disturbed, run with great swiftness, and may often be seen in
hotbeds and fermenting dung prowling in search of the stercorarious
beetles. But the most remarkable insect of this kind is the _Uropoda
vegetans_: it derives its nutriment from the insects it assails not
by its _mouth_, but by means of a long _anal pedicle_ by which it is
attached to them. De Geer found these in such numbers upon a species
of _Leptura_, that its whole body was almost covered with them; they
hung from the legs and antennæ in bunches, and gave the animal a most
hideous and disgusting appearance. Under this load of vermin it could
scarcely walk or move, and all its efforts to get rid of them were in
vain: many were attached to its body and to each other by their anal
pedicles, but others had cast them off and were walking about. When
put into a glass with earth, they began to abandon their prey, so
that in a few days it was quite freed from its plagues. He found that
these parasites lived long in alcohol[1007].
If you inquire--How are these mites originally fixed by their
pedicles? it seems most probable, that as the _Hemerobii_, when they
lay their eggs, know how to place them upon a kind of footstalk, so
the parent _Uropoda_ has the same power; and this pedicle appears to
act the part of an umbilical chord, conveying nutriment to the fœtus
not from a _placenta_, but from the body of the insect to which it
is attached; till having thus attained a certain maturity of growth
and structure, it disengages itself and becomes locomotive. Many eggs
of the aquatic _Acarina_ (_Hydrachna_, &c.) are also furnished with
a short pedicle by which they are fixed to _Dytisci_ and other water
insects. De Geer found some of this description on the underside of
the water-scorpion, so thickly set as to leave no void space: they
were oval, of a very bright red, and of different sizes on different
individuals; whence it was evident that they grow when thus fixed:
when hatched or released--for perhaps they may be regarded as fœtuses
in their _amnios_ rather than eggs--they cease to be parasitical.
Let us admire on this occasion, (piously observes this great
Entomologist,) the different and infinitely varied means by which the
AUTHOR of Nature has endowed animals, particularly insects, for their
propagation and preservation: for it is a most extraordinary sight to
see eggs grow, and pump as it were their nutriment from the body of
another living animal[1008]. As these mites are fixed to the _crust_
as well as its inosculations, they must have some means of forcing
their nutriment through its pores.
Another insect, remarkable for its resemblance in some respects
to the scorpion--called in this country the book-crab (_Chelifer
cancroides_), from its being sometimes found in books--occasionally
is parasitic upon flies, especially the common blue-bottle-fly
(_Musca vomitoria_). They adhere to it very pertinaciously under
the wings; and if you attempt to disturb them, they run backwards,
forwards, or sideways, with equal facility.
Spiders also are infested by mites. Mr. Briggs once found a very
small _Theridion_, to the thorax of which were attached four oblong
bright scarlet mites, each of which was as large as the thorax
itself. He afterwards met with another spider still smaller, attacked
by two of these swoln parasites, one of which appeared to him nearly
equal to the spider in size. This mite was probably either _Leptus
Phalangii_, or _Astoma parasiticum_.
2. We now come to a perfectly distinct tribe of insect parasites,
which belong to that section or order of intestinal _worms_ which
Rudolph has denominated _Entozoa nematoidea_, and Lamarck _Vers
rigidules_[1009]. To this tribe belong the _Gordius_ of Linné and
the _Filaria_ of modern zoologists, which from the experiments and
observations of De Geer, Dr. Matthey, &c. appear to have been too
hastily separated, being really congenerous, and living indifferently
in water and in the intestines of insects and other animals[1010].
To this genus belong the guinea-worm (_Gordius medinensis_[1011]),
the _Furia infernalis_, and several others that are found in various
vertebrate animals. These little worms have been discovered in insects
of almost every Order; and their attack generally produces the death
of the animal, though they appear not to devour those parts that are
essential to life[1012]. I once took a specimen of _Pœcilus azureus_,
and upon immersing it in boiling water I was surprised to see what
at first I mistook for an intestine, thrust itself forth; but upon a
nearer inspection, to my great surprise I found it was one of these
worms, thicker than a horse-hair and of a brown colour. Mr. W. S.
MacLeay also once found one in _Abax Striola_. It still remains in my
specimen, making it appear as if it had a long tail. De Geer long ago
found these worms in grasshoppers[1012]; but Dr. Matthey has given the
fullest account of one which infested _Acrida viridissima_. A friend
of his noticing one of these insects which had not strength enough to
leap and could scarcely even walk, being struck with the circumstance,
caught the animal, upon which its hind legs were immediately detached
from it. His surprise was greatly increased when he saw issue from its
body a cylindrical worm about two feet and a half in length. Upon being
called, Dr. M. soon recognised it for a _Gordius_ or _Filaria_; and on
his putting it into water, it moved in it with great velocity, twisting
its long and slender body in all directions. Upon opening the body of
the grasshopper, nothing appeared within it but the intestine shrunk
up to a thread. A few days after, another was brought, which appeared
in full vigour, but its abdomen was enormously distended, and from it
another worm was extracted, which remained without motion rolled in a
spiral direction: intending to preserve this in spirits of wine--as it
had become flat he first immersed it in water, that it might recover
if possible its cylindrical form. Upon immersion a movement took place
in the animal, and it gradually recovered its plumpness; but it still
remained without motion, as if dead, for nearly five days, when another
living specimen being brought and placed with it, as soon as water
was poured on them, the seemingly dead one began to show by a slight
oscillation in its extremities that life was not extinct in it. Fresh
water being poured upon it, at the end of the day it had recovered
all its strength and agility. He afterwards often repeated the same
experiment with a similar result[1013]. From this account it appears
that the _Gordius_ or _Filaria_ has a property resembling that of the
_Vibrio Tritici_, so well described and so beautifully figured by M.
Bauer[1014], of apparently dying and being resuscitated by immersion in
water. How long it can retain this property remains to be ascertained.
De Geer states that he had seen them of the length of two feet[1015];
but they vary considerably in this respect. In ants, in which Gould
detected them, he states their length to be not more than half an
inch[1016]. In caterpillars, which they sometimes infest, they are
longer; in that of _Notodonta Ziczac_, De Geer found one three inches
and a half long[1017]; and Rösel three, of six inches, in that of
_Deilephila Euphorbiæ_[1018]; and in _Phalangium cornutum_, according
to Latreille, they extend to more than seven inches[1019]. In the larva
of a _Phryganea_ L. the author first named found one which was more
than a foot long, corresponding exactly with the _Gordius aquaticus_
of Linné; being forked at one extremity, brown above, gray below, and
black at each end[1020]. These animals _appear_ to die as soon as they
leave the body[1021] they have preyed upon; except this happens in
water, when their activity has no repose. In this element they give
their bodies every possible inflexion, often tying themselves in knots
in various places, interlacing and twisting themselves in a hundred
different ways; so that when confined in the body of an insect, from
their extreme suppleness and power of contortion they find sufficient
space wherein to pack their often enormous length[1022]. Linné makes
one of their habitats clay; and Mr. W. S. MacLeay finds them very
common at Putney in clay at the bottom of pools.
Dr. Matthey asks--How does the _Gordius_ get into _Acrida
viridissima_[1023]? And De Geer--Why do they die after having quitted
a caterpillar? and where do they perpetuate their species[1024]?
These questions, without further observations, cannot easily be
answered. However, it may be supposed that carnivorous insects, such
as _Harpali_, &c. may swallow them when found apparently dead in
clay, where the water has been evaporated, or when they have been
ejected by other insects; and they may revive in their bodies, as Dr.
Matthey found them to do in water. It is not difficult to conjecture
that the larvæ of _Phryganeæ_ may meet with them when young in the
water, and sometimes unluckily swallow them with their food. Why they
become as dead when they emerge from their prey we cannot at present
conjecture; but no doubt to answer some wise purpose;--in rainy
seasons they probably revive and get into little hollows full of
rain-water. Upon De Geer's last question--How they perpetuate their
species--at present I can offer no conjecture.
I am, &c.
FOOTNOTES:
[918] _Ps._ civ. 29.
[919] _Hist. Animal._ l. viii. c. 27.
[920] _The Principles of Botany and of Vegetable Physiology_, § 310-353.
[921] Dr. Leach, from a communication of Sir Joseph Banks, has given
a very interesting history of a spider which, having lost five of its
legs, from a web-weaver had become a hunter; these legs it afterwards
reproduced, though shorter than the others. _Linn. Trans._ xi. 393.
Comp. _N. Dict. d'Hist. Nat._ ii. 282.
[922] VOL. I. p. 55--.
[923] VOL. II. p. 166--.
[924] Huber _Abeilles_ ii. 409.
[925] _N. Dict. d'Hist. Nat._ i. 42.
[926] De Geer i. 72--.
[927] Reaum. iv. 342.
[928] _Naturf._ xii. 224. _t._ v. _f._ 8.
[929] _Naturf._ xvi. _t._ iv. _f._ 1-3.
[930] Huber _Fourmis_, 174. note 1.
[931] VOL. II. p. 365.
[932] _N. Dict. d'Hist. Nat._ i. 42.
[933] De Geer vi. 75. Latr. _Hist. Nat._ xiv. 371.
[934] Jacquin _Collectan._ iii. _t._ xxiii. _f._ 7.
[935] De Geer _ubi supr._
[936] Dr. Bevan asserts (_The Honey-bee_, 197) "that we have no
evidence that pollen constitutes any part of the food of _adult_ bees."
Had he consulted Reaumur (v. 418) he would have found that this great
man examined the proceedings of a bee with a magnifying glass, and
distinctly saw her devour very deliberately the masses of pollen on her
hind legs. He says also (Ibid. 419.) that if the stomach and intestines
are opened, they will be found filled with that substance.
[937] Schirach _Hist._ &c. 54. Reaum. v. 713. _N. Dict. d'Hist. Nat._
i. 42.
[938] _N. Dict. d'Hist. Nat._ i. 42. Schirach _Hist._ 56.
[939] Latr. _Hist. Nat._ xiv. 163--. _N. Dict. d'Hist. Nat._ iv. 134--.
[940] _Œuvr._ ii. 48--.
[941] Lesser L. ii. 121.
[942] _Synops. Meth. Fung._ 687. _g._ 63. _n._ 1, 2.
[943] _Ibid._ 4. _g._ 1. _n._ 4.
[944] VOL. III. p. 335--.
[945] VOL. I. p. 267--.
[946] _Mon. Ap. Angl._ ii. 111. _Linn. Trans._ xi. 90--.
[947] Reaum. ii. 439.
[948] _Ibid._ 415. Mouffet 57.
[949] _Hist. Ins._ Præf. xv.
[950] _Cat. Cant._ 137.
[951] See above, p. 162--.
[952] Reaum. vi. 306.
[953] _Fn. Suec._ 1626.
[954] _Linn. Trans._ iii. 26.
[955] De Geer i. 608. Linné has made a mistake with regard to the
Ichneumon here alluded to, in calling De Geer's saltatorious Ichneumon
_I. Muscarum_, and referring for it to _t._ xxxii. _f._ 19, 20 of that
author; whereas the Ichneumon that preys upon the aphidivorous flies
does not jump, and is figured by De Geer 605. _t._ xxxiv. _f._ 26-29.
The jumping one feeds on the larva of a _Coccinella_.
[956] Vallisnieri _Lettere_, &c. 80.
[957] Reaum. vi. 296--.
[958] Linné evidently has described another species under _I.
Ovulorum_, in _Fn. Suec._ 1644.
[959] De Geer i. 593--.
[960] _N. Dict. d'Hist. Nat._ vi. 10.
[961] Geoffr. _Hist. Ins. Par._ ii. 361.
[962] _Linn. Trans._ v. 102--.
[963] PLATE XX. FIG. 22. _a._
[964] De Geer ii. 850--.
[965] Reaum. ii. 444--.
[966] De Geer ii. 863--.
[967] Panzer _Fn. Germ. Init._ lxxii. 4.
[968] De Geer, i. 583--. ii. 822--. 907.
[969] Reaum. vi. 312.
[970] Leeuwenh. _Epist._ Oct. 6, 1700. De Geer ii. 869.
[971] _Ibid._ i. 604.
[972] Rai. _Hist. Ins._ 259--.
[973] See above, p. 217; and VOL. I. p. 356.
[974] _Ibid._ 348.
[975] Reaum. vi. 303--.
[976] Reaum. ii. 454--.
[977] De Geer ii. 879--.
[978] _N. Dict. d'Hist. Nat._ xvii. 513.
[979] De Geer vi. 411--.
[980] VOL. I. p. 172.
[981] _Linn. Trans._ iv. 236.
[982] VOL. I. p. 50--. 170--. Since that Volume of the present
Edition was printed, Say's account of the Hessian Fly has been met
with, where he distinguishes it by the above name. (_Journal of the
Acad. of Nat. Sciences of Philadelphia_ 1817.) The Ichneumon he calls
_Ceraphron Destructor_.
[983] De Geer, i. 605. This, as before observed, is not the _I.
Muscarum_ of Linné; but it ought to have that name, and the other
instead to be named, _I. Coccinellæ_.
[984] _Ent. Carn._ 760, 761.
[985] De Geer i. 587.
[986] _Ibid._ ii. 876.
[987] Reaum. ii. 417--.
[988] Reaum. ii. 419--.
[989] De Geer i. 583--.
[990] _Ibid._ ii. 884.
[991] See above, p. 164.
[992] Reaum. vi. 312.
[993] VOL. I. p. 99.
[994] De Geer _ubi supr._
[995] _Ibid._ 883.
[996] _Linn. Fn. Suec._ 1609.
[997] Reaum. ii. 443. De Geer i. 196--, 550--. vi. 24.
[998] Reaum. ii. 440--.
[999] VOL. I. p. 99.
[1000] Ibid. 84, 97.
[1001] VOL. I. p. 163. note^c. VOL. III. p. 162. note^b.
[1002] De Geer v. 8--.
[1003] _Naturf._ xxiii. _t._ i. _f._ 8.
[1004] _N. Dict. d'Hist. Nat._ xx. 110--.
[1005] _Ent. Carn._ 1052-4.
[1006] _Hister_ particularly.
[1007] De Geer vii. 126--.
[1008] De Geer vii. 144--.
[1009] Lamarck _Anim. sans Vert._ iii. 196.
[1010] De Geer ii. 554--. Pictet _Bibliotheq. Univers._ num. ult.
[1011] The existence of this animal has been satisfactorily
ascertained by M. de Blainville, who had a specimen, extracted from a
human body, sent him by M. Girard, a surgeon of Guadaloupe.
[1012] De Geer ii. 555.
[1013] Matthey _ubi supr._
[1014] _Philos. Trans._ 1823. 8. _t._ i. ii.
[1015] De Geer ii. 556.
[1016] Gould _Ants_, 63.
[1017] De Geer i. 551.
[1018] Rösel I. iii. 20.
[1019] Latr. _Fourmis_, 373.
[1020] De Geer ii. _ubi supr._ _t._ xiv. _f._ 12-14.
[1021] _Ibid._ i. 553.
[1022] Ibid. ii. 556. _t._ xiv. _f._ 12, 13.
[1023] _Ubi supra._
[1024] De Geer i. 553.
LETTER XLV.
_SENSES OF INSECTS._
At first one would think that the _senses_ of insects might be
described in very few words, and scarcely afford matter for a
separate letter; but when we find that physiologists are scarcely
yet agreed upon this subject, and that the use of some of their
organs, which appear to be organs of sensation, has not yet been
satisfactorily ascertained--we shall not wonder that it requires more
discussion than at the first blush we were aware of. In treating on
this head I shall first say something on the senses in _general_, and
then confine myself to those of insects.
Touch, taste, smell, hearing, and sight, I need not tell you, is
the usual enumeration of the senses: but as the term includes every
means of communication with the external world, the list perhaps
might be increased; and there is ground for thinking that the number
_seven_, so signalized as a _sacred_ number[1025], may also here
have place. Dr. Virey, an eminent physiologist, whose sentiments
on various subjects I have before noticed with approbation[1026],
appears to be of opinion that there are really _seven_ senses; which
he divides into those that are altogether _physical_, and those that
are more connected with the _intellect_. The first of these divisions
contains _four_ senses,--touch, love, taste, and smell;--the second
_three_,--hearing, sight, and the internal sense of thought, or the
brain[1027]. That he is right in adding _love_ to the list seems to
me evident, because it is as distinct from _touch_, as _smelling_ and
_taste_ are. With regard to the other, though it may be expected that
there should be a transitive sense connecting the intellect (if I may
so speak) with the external organ of sense, and as a medium by which
the former can receive the notices of the external world furnished by
the latter; yet it seems improper to make the _entire brain_ itself
a _sense_. We know that the agent between the common sensory and the
sense is the consciousness or _perception_ of the impression. "Seeing
we may see and not _perceive_, and hearing we may hear and not
_understand_." The picture may be painted upon the retina of the eye,
the sound may strike upon the tympanum of the ear; but neither the
one nor the other be received by the intellect, unless the internal
power or faculty of perception be in action and mediate between them.
This is what I mean by the _internal sense_, which, to use a term of
Mr. W. S. MacLeay's[1028], is _osculant_ between intellect and sense,
or forms the transit from one group of powers to the other.
Of the ordinary senses, _sight_ holds the first rank: it can dart
to the region of the stars, and convey by the perceiving sense, to
the sensory, ideas of innumerable objects. Next in rank is _hearing_,
which can receive sounds from a great distance; but the ideas it
remits are confined only to one object, the variations of tones. In
the other organs the sensitive power is much more confined. There is
another difference between the intellectual and physical senses:--the
former are the only ones that receive and convey sensations of the
beautiful and sublime; of harmony and discord,--the latter, though
they minister more to our sensual enjoyments, add little to our
intellectual; and therefore too devoted an indulgence in them debases
our nature, and levels us with the brutes, which use their eyes and
ears only for information, not for pleasure[1029].
In man the ordinary five senses are usually in their greatest
perfection, although in some animals particular senses have a greater
range. The Vertebrates in general are also gifted with the same
number, though there are some exceptions. But in the _Invertebrates_
they are seldom to be met with all together in the same object. The
_Cephalopods_ have no _smell_. Several _Gasteropods_ can neither
_hear_ nor _see_. The animals of bivalve shells have neither eyes,
nor ears, nor smell; and the zoophytes and the races below them have,
it is affirmed, only the single sense of _touch_, which in them is so
extremely delicate as to be acted upon even by _light_[1030].
Not so our insects. These, there is good reason to believe, possess
all the ordinary senses. That they can _see_, _touch_, _taste_, and
_smell_, no one denies. Linné and Bonnet, however, thought them
deprived of _hearing_[1031]; but numerous observations prove the
contrary. That they hear in their _larva_ state, is evident from
facts stated by the latter physiologist. He found that the sound of
his voice evidently affected some caterpillars; which he attributes,
but surely without reason, to the delicacy of their sense of touch:
at another time, when some caterpillars of a different species were
moving swiftly, he rang a small bell; upon which they instantly
stopped and moved the anterior part of their body very briskly[1032].
That they possess this faculty in their _imago_ state is confirmed
still more strongly by facts. I once was observing the motions of an
_Apion_ under a pocket microscope: on seeing me it receded. Upon my
making a slight but distinct noise, its antennæ started: I repeated
the noise several times, and invariably with the same effect. A
_Harpalus_, which I was holding in my hand, answered the sound in
the same manner repeatedly. Flies, I have observed, at brisk and
distinct sounds move all their legs; and spiders will quit their
prey and retire to their hiding places. Insects that live in society
give notice of intended movements, or assemble their citizens for
emigration by a certain _hum_[1033]. But the most satisfactory proof
of the hearing of these animals is to be had from those _Orthoptera_
and _Hemiptera_ whose males are vocal. Brunelli kept and fed several
males of _Acrida viridissima_ (a grasshopper with us not uncommon)
in a closet, which were very merry, and continued singing all the
day; but a rap at the door would stop them instantly. By practice he
learned to imitate their chirping: when he did this at the door, at
first a few would answer him in a low note, and then the whole party
would take up the tune and sing with all their might. He once shut up
a male in his garden, and gave the female her liberty; but as soon as
she heard the male chirp, she flew to him immediately[1034].
But although physiologists are for the most part agreed that insects
have the ordinary five senses of vertebrate animals, yet a great
variety of opinions has obtained as to their external organs; so that
it has been matter of doubt, for instance, whether the _antennæ_ are
for smell, touch, or hearing; and the _palpi_ for smell, taste, or
touch. Nor has the question, as it appears to me, been satisfactorily
decided: for though it is now the most general opinion that the
primary use of antennæ is to _explore_ as _tactors_, yet by the
most strenuous advocates of this opinion they are owned not to be
_universally_ so employed; so that granting this to be _one_ of
their principal functions, yet it seems to follow that there may
be _another_ common to them all, which of course would be their
_primary_ function. We are warned, however, not to lay any stress
upon the argument to be drawn from analogy; and told that we might as
well dispute about the identity of the nose of a man, the proboscis
of the elephant, the horn of the rhinoceros, the crest of the cock,
or the beak of the toucan[1035]. But this is merely casting dust
in our eyes: for though three of these are _nasal_ organs, bearing
_nostrils_; the two others have no relation to the question, the
horn of the rhinoceros and the crest of the cock being merely
_appendages_, and have no more analogy to the nose and nostrils,
which co-exist with them, than they have to the eyes or ears. I have
on a former occasion observed, that a gradual change sometimes takes
place in the functions of particular organs; but still, generally
speaking, this observation regards _secondary_ functions--the
_primary_ usually remaining untouched. We may say, for instance,
with regard to the primary use of the _legs_ of animals, that it is
locomotion; while the secondary is either walking, running, jumping,
flying, or swimming, according to the circumstances and nature of the
animal. Thus the _fore-legs_ of the _Mammalia_, in _birds_ become
_wings_, and both pair in _fish_ are changed to _fins_. Observe, I do
not say _always_ and invariably, but in most cases,--that analogous
parts have analogous uses, at least as far as _primary_ uses are
concerned. When, therefore, we cannot have demonstrative evidence
concerning the function of an organ discoverable in any animal, we
may often derive satisfactory probable arguments from the analogies
observable in their structure compared with that of other animals,
concerning the nature of whose organs we have no doubt. In fact,
the chief evidence we have with regard to the office of the organs
of sense in the animals immediately below ourselves, is that of
analogy;--because _we_ see with our eyes, hear with our ears, &c., we
conclude, with reason, that _they_ do the same.