Imágenes de páginas
PDF
EPUB

6

this insect, more satisfactory than the preceding ones of Bonnet. He kept several in a chamber, which continued their crinking song through the whole day; but the instant they heard a knock at the door, they were silent. He subsequently invented a method of imitating their sounds, and when he did so outside the door, at first a few would venture upon a soft whisper, and by and bye the whole party burst out in chorus to answer him ; but upon repeating the rap at the door, they instantly stopped again as if alarmed. He likewise confined a male in one side of his garden, while he put a female on the other at liberty, which began to leap as soon as she heard the crink of the male, and immediately came to him, an experiment which he frequently repeated with the same result. It is remarkable that the males alone of these insects are musical; for “ the females," as Swammerdam long ago observed, “ of locusts, grasshoppers, and others, make no noise.” We may, in passing, request our readers to remark that Brunelli's insect has very long antennæ.

It seems to be not illogical to infer, from the variety of sounds produced by insects, that, in the instance in question, as well as in many others, they are intended for signals to their companions, who, of course, must possess organs of hearing. The drum or instrument by which the last-mentioned insect produces its loud music has been described by De Geer, and subsequently by Lichtenstein. “Our male green field-hoppers,” says the former, “ in that part of the right wing-case which is folded horizontally over the trunk, have a round plate, made of very fine transparent membrane, resembling a little mirror or piece of talc, and as tense as a drum. It is surrounded by a strong and prominent nervure, but is concealed under the fold of the left wing-case, where also there are strong nervures corresponding to what may be called the hoop of the drum. It is exceedingly probable that the quick motion with which the insect rubs these nervures against each other, produces a vibration in the membrane, whence the sound is augmented." By alternating the motion rapidly from right to left, the sound is produced in an almost continued strain, as we have remarked in those we have kept in our study; while in the crickets, who alternate the motion more slowly, the sound is omitted at interrupted intervals, a remark which any person may readily verify.

The grasshoppers and locusts produce their chirp by applying the hind shank to the thigh, rubbing it smartly against the wing-case, and alternating the right and left legs. They have also a drum like the preceding family for augmenting the sound. “ On each side,” says De Geer, “ of the first segment of the abdomen, immediately above the origin of the hind thighs, there is a large deep opening, somewhat oval in form, and partly closed by an irregular flat plate or lid, of a hard substance, but covered by a flexible, wrinkled membrane. The opening left by the lid is in form of a half-moon, and at the bottom of the cavity is a white membrane, shining like a mirror, and tensely stretched. On the side of the opening, towards the head, there is a small oval hole, into which the point of a pin may easily pass; and when the membrane is removed, a large cavity is brought into view. The whole of this apparatus seems to contribute much both to produce and to increase the sound caused by the insects.”

• We have examined the hole mentioned by De Geer, in a number of individuals, and have been struck with its resemblance to the hole in a military drum, as well as in violins and guitars. We found, indeed, upon

stopping up this hole with a bit of wafer, that the insect could no longer produce its peculiar sound, but only a sort of muffled scraping. Swanmerdam was acquainted with this instrument, though he does not mention the hole. “The grasshopper," he says, “has two peculiar small drums, like the drum of our ear, which being struck by the help of two lunulated cartilages vibrate the air in such a manner as to produce the sound.”

“The crickets, another family of this order of insects, are well known for their chirping-song, which, associated as it is either with the snug chimney-corner, or the sunshine of summer, affords a pleasure which certainly does not arise from the intrinsic quality of its music. Sounds,” it is well observed by White, “ do not always give us pleasure according to their sweetness and melody; nor do harsh sounds always displease. Thus the shrilling of the field-cricket, though sharp and stridulous, yet marvellously delights some hearers, filling their minds with a train of summer ideas of every thing that is rural, verdurous, and joyous."

“ Sounds unharmonious in themselves and harsh,

Yet heard in scenes where peace for ever reigns,
And only there, please highly for their sake.'

CowPER, Task, book i. • This circumstance, no doubt, causes the Spaniards to keep them in cages, as we do singing-birds. White tells us, that, if supplied with moistened green leaves, they will sing as merrily and loud in a paper cage as in the fields; but he did not succeed in planting a colony of them in the terrace of his garden, though he bored holes for them in the turf to save them the labour of digging.

Swammerdam entertained a different notion of their music. member,” says he, " that I once saw a whole field full of these singingcrickets, each of which had dug itself a hole in the earth two fingers deep, and then, sitting at the entrance thereof, they made a very disagreeable noise with the creaking and tremulous motion of their wings: when they heard any noise they immediately retired with fright into their little caverns."

* The hearth-cricket, again, though we hear it occasionally in the hedge banks in summer, prefers the warmth of an oven or a good fire, and thence, residing as it were always in the torrid zone, is ever alert and merry, a good Christmas fire being to it what the heat of the dog-days are to others. Though crickets are frequently heard by day, yet their natural time of motion is only in the night. As soon as it becomes dark, the chirping increases, and they come running forth, and are often to be seen in great numbers, from the size of a flea to that of their full stature. Like the fieldcricket, they are sometimes kept for their music; and the learned Scaliger took so great a fancy to their song that he was accustomed to keep them in a box in his study. It is reported, that in some parts of Africa they are kept and fed in a kind of iron oven, and sold to the natives, who like their chirp, and think it is a good soporific. Milton chose for his contemplative pleasures a spot where crickets resorted ::

" Where glowing embers through the room

Teach light to counterfeit a gloom,
Far from all resort of mirth,
Save the cricket on the hearth."--Il Penseroso.

66 I re

• We have been as unsuccessful in transplanting the hearth-cricket, as White was with the field-crickets. In two different houses we have repeatedly introduced crickets, but could not prevail on them to stay. One of our trials, indeed, was made in summer, with insects brought from a garden wall, and it is probable they thought the kitchen fire-side too hot at that season.

• The instrument upon which the male-cricket plays (for the female is mute) consists, as in the preceding case, of strong nervures or rough strings in the wing.cases, by the friction of which against each other a sound is produced and communicated to the membranes stretched between them, in the same way that the vibrations caused by the friction of the finger upon the tambourine are diffused over its surface.'--pp. 76–82.

The hum of bees, Swammerdam supposes, proceeds from the motion of the wings alone, particularly the small membraneous wings at the shoulder, which is increased by the internal air

propelled from the air tubes that lie beneath them. White, the justly celebrated naturalist of Selborne, remarked frequently, in hot summer days, on a down in his neighbourhood, sound like that of many bees humming in the air, though not one of these insects was to be seen at the time. Mr. Rennie observed the same humming in the neighbourhood of London, which he could no more explain than White, until he saw, upon one occasion, a troop of swallows busily hawking high overhead where the humming was heard, a circumstance from which he reasonably inferred that the noise proceeded from insects invisible from the distance at which they were collected. The same sound may be heard in the summer evenings by any person who chooses to walk into the fields that lie between Kentish Town and Hampstead. We have often listened to it, mingled with the lowing of cows, the occasional barking of dogs, and the confused murmur that now and then is borne on the air from the metropolis, with feelings of mystic delight. Mr. Knapp confirms this explanation. “That purely rural, little noticed, and, indeed, local occurrence,” he says, “called by the country people hummings in the air, is annually heard in one or two fields near my dwelling. About the middle of the day, perhaps from twelve o'clock till two, on a few calm sultry days in July, we occasionally hear, when in particular places, the humming of apparently a large swarm of bees. It is generally in some spacious open spot that this murmuring first attracts our attention. - As we move onward, the sound becomes fainter, and by degrees is no longer audible. That this sound proceeds from a collection of bees, or some such insects high in the air, there can be no doubt; yet the musicians are invisible. At these times, a solitary insect or so may be observed here and there, occupied in its usual employ, but this straggler takes no part in our ærial orchestra.”

Naturalists differ much as to the vision of insects, some maintaining with Bidloo that no animal is naturally blind, others that several species of insects are altogether deprived of eyes. Latreille

mentions two species of very small ants, in which he could never discover any organ of vision. One of the classes of the white ants is generally considered to be blind. According to some naturalists the bee is very short sighted ; according to others, the sight of that insect is the most perfect of all others. The former notion seems to have been adopted by Mr. Rogers, when he wrote the following lines in his " Pleasures of Memory :”—

• “ Hark! the bee winds her small but mellow horn,

Blithe to salute the sunny smile of morn.
O’er thymy downs she bends her busy course,
And many a stream allures her to its source.
'Tis noon, 'tis night. That eye, so finely wrought
Beyond the search of sense, the soar of thought,
Now vainly asks the scenes she left behind;
Its orb so full, its vision so confined !
Who guides the patient pilgrim to her cell ?
Who bids her soul with conscious triumph swell?
With conscious truth retrace the

mazy

clue
Of varied scents that charmed her as she flew ?
Hail ! Memory, hail! thy universal reign

Guards the least link of being's glorious chain." - p. 122. The memory of the bee, however, is but a very short one, for any person may observe it visiting repeatedly the flower which it had already rifled of all its treasure. Mr. Rennie is indebted to Réaumur fór a solution of these contradictory opinions :

• If Réaumur, however, be correct in his opinions, as we are inclined to think he is, these apparent discrepancies may be easily reconciled; for he attempts to show, that bees and most other insects are endowed with two sorts of eyes, one for distant and another for near vision : instead of having the power as we have of adapting the eye to various distances, the nature of which adaptation is not well understood. In order to understand this more precisely, it will be necessary to enter into a few details as to the number and structure of the eyes of insects.

. It may at first appear not a little puzzling to conceive how a spider with eight eyes, a centipede with twenty, and a butterfly with thirty-five thousand facets in its two eyes, can perceive only one object; yet the difficulty is not of a very different kind from that of our own two eyes representing only a single object and not two,-a subject which has exercised the ingenuity of many a philosopher. Vandermonde, for example, supposed that children at first see double, and correct the error by experience; an opinion adopted by Blumenbach : Dr. Reid referred it to an original and inexplicable law of human nature, confessing thereby his inability to explain it ; and some of the old philosophers satisfied themselves that it was because the nerve from each eye meets before reaching the brain. The latter would have perhaps been satisfactory, had it not been refuted by the simple experiment of pushing one of the eyes a little aside, when objects will be seen double, though this cannot alter the meeting of the nerves. Dr. Wells explains it by the coincidence of what he calls the visible direction.

• Whatever opinion be adopted, it is evident that most creatures can see an object by using one eye only, sometimes better than when both are employed. The celebrated painter, Leonardo da Vinci, upon this principle recommended his pupils always to look at distant objects with one eye only, and we have frequently observed in birds, particularly those which feed on insects, that on looking out for prey, they most commonly turn their head on one side, so as to bring only one eye to bear on the object. A thrush always does so when he examines a snail-shell that he means to attack, and a red-breast before he pounces upon a worm. It is no doubt for this very reason that the wryneck is enabled to move its head in the manner from which it derives its popular name; and many insects, such as the dragon-flies, can turn their heads nearly round about; though, from the great volume of their eyes, this might almost be considered superfluous.

*

he says,

Independently, however, of the anatomical structure, of which from the minuteness of the parts there might be considerable doubt, the experiments of Réaumur appear to settle the point.

" I have varnished those eyes,” or what amounts to the same, I varnished the back part of the head in more than twenty bees, which I then set at liberty, three or four paces from the hive; but not one of them knew where to find it again, nor appeared to search for it. They flew at random towards the adjacent plants, but never to a distance, and though they seemed to have no difficulty in flying, I never saw them rise in the air as those do whose facetted eyes

I had varnished over.” The latter observation seems to prove that the coronet-eyes are appropriated to upward vision ; while we may suppose the facetted eyes to be for horizontal vision, and for looking downwards. Kirby, indeed, has distinguished a whole genus from the circumstance of its being thus furnished with two pair of eyes. One species of this is found in the vicinity of London.

• Fabricus, who is followed by Olivier, considers one pair of these eyes as nothing more than a spot; but accurate examination shows that the principal facetted eyes are actually divided by the crossing of the corner, which in other insects of this family only enters, and indents a portion of the eye without dividing it entirely. What is not less singular, the males of more than one species of day-fly, besides the regular number of facetted and coronet eyes, have a pair of facetted eyes on the top of a short columnar projection.

In the little whirlwig that skims about so merrily on standing water, the upper portion of the eyes, fitted for seeing in the air, is placed on the upper part of the head, and the lower portion, fitted for seeing in water, in the lower part, a thin division separating the two.

• When a facetted eye, such as that of a butterfly, is examined a little closely, it will be found to have the appearance of a multiplying glass, the sides, or facettes, resembling a brilliant cut diamond. Puget adapted the eye of a flea in such a position as to see objects through it by means of a microscope, and nothing could exceed the singularity of the exhibition. “ A soldier, who was seen through it, appeared like an army of pigmies ; for while it multiplied it also diminished the object: the arch of a bridge exhibited a spectacle more magnificent than human skill could perform; and the flame of a candle seemed the illumination of thousands of lamps." Leeuwenhoeck, in the same manner, looked through the eye of a dragon

« AnteriorContinuar »