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convenient method of scientific exposition; and the attempt to identify it with the atheistic archetypes of Robinet, is pitifulwe had almost said, malignant. Mr. Rennie has been recently appointed to a professorship in King's College:—can this ultra sensitiveness have any connexion with that promising appointment? We are, however, glad to turn from this miserable business to matter more attractive; and the following extract will shew the vigilance with which Mr. Rennie observes, and the interesting manner in which he describes.
In a colony of bank-swallows, near Charlton, in Kent, consisting of more than a hundred pairs, not more than two or three pairs of sparrows
have settled; I say “ settled ", because they appear to live on terms of good neighbourhood with the original colonists, as I hare watched them for hours passing and repassing without the least indication of hostility, which amongst birds soon shews itself in tones of insult and defiance, and by incessant skirmishing and bickerings. How differently these same bank-swallows treated a poor cuckoo, I had an opportunity of witnessing, while observing their good fellowship with the sparrows. The cuckoo was flying quietly along, certainly meditating no harm against the swallows, and not even poaching on their domain by hawking for flies, inasmuch as he prefers a breakfast of caterpillars, which the swallows never touch ; nevertheless, the instant he appeared, the tocsin was sounded, and every swallow in the colony darted out of the holes to pounce upon the intruder, whom they beat most unmercifully with bill and wing, till they drove him from their boundaries. The sparrows, meanwhile, sat at the mouths of their holes with the utmost nonchalance as spectators altogether unconcerned in the affray. I have mentioned this harmonious consociality of the bank-swallows and the sparrows, the rather, because we meet with anecdotes in books, of obstinate contests for possession between sparrows and other species of swallows. Avicenna, and afterwards
, Albertus Magnus, tell us, that when a sparrow takes forcible possession of the nest of a window-swallow, there ensues determined battle between the proprietors and the invaders, in which the latter usualiy come off in the first instance victorious, from their cunningly remaining in the nest. The swallows, however, take care to be revenged; for, summoning in their companions to assist them, they bring a quantity of the mortar which they use in building their nests, and closing up the entrance, entomb the sparrows alive. The same story is giren by Rzaczynski: and Batgouski, the jesuit, affirms that he was an eyewitness of the circumstance; while Linnæus, who was much tou credulous of such matters, states it as a fact ascertained. M. Montbeillard, on the contrary, says, that the instances which he has witnessed of contests of this kind give no countenance to the story. He observed the swallows, indeed, return frequently in the course of the summer, to quarrel with the sparrows, and often wheeling about for a day or two; but they never attempted to enter the nests, or to shut them up with mortar.' The whole account, indeed, I should say, is a romancing legend; for the sparrows, with their strong bills, would instantly de molish the thickest wall which the swallows could build, instead of quietly permitting themselves to be imprisoned, as the above veracious writers have chosen to report.'
The Insect Miscellanies' form the third volume of that interesting and valuable series which makes a part of the Library . of Entertaining Knowledge', and which, under the titles of • Insect Architecture', Insect Transformations, and Insect • Miscellanies', comprises a larger mass of sound practical information on the subject of Entomology, than is to be found elsewhere within thrice the compass. There is no rubbish ; no attempt to bolster up a favourite system by the invention or perversion of facts; no flourish or fine writing ; none of that intolerable prosing which makes the comprehensive and invaluable work of Kirby and Spence so heavy and unreadable: all is clear and compressed, shrewd and business-like. Nor could we name, on any subject, three volumes of similar size, so thoroughly charged with instruction.
The present volume treats of the Senses of Insects; their Food; their Social and Domestic Habits; and concludes with some valuable directions relating to the collection and preservation of insects, and an account of the various systematic arrangements. The volume on Insect Architecture was noticed at some length in our pages * We shall now confine ourselves to a single specimen of Insect Transformations, as furnished by the natural history of the bombyx or silk-worm.
This wonderful little workman proceeds from a yellow egg of about the size of a grain of mustard-seed, which is deposited, during the summer, by a greyish moth of the genus phalænæ. When first hatched, it appears as a small black worm about a quarter of an inch in length, weighing the hundredth part of a grain. In the course of thirty days, it will consume above an ounce of mulberry leaves; that is to say, it devours in vegetable substance about 60,000 times its own primitive weight. Within the same period, its length increases to about forty times its first measurement, and its weight is multiplied many thousand fold. A hundred worms just hatched weigh about a single grain ; and, on attaining their greatest size and weight, 9500 grains. But even this increase of weight is inconsiderable, when compared with that of the caterpillar of the goat-moth, which is said to become 72,000 times heavier than when newly hatched. This fact is not, however, more wonderful than that an ostrich nine feet high and weighing 150lbs., should be produced from an egg about the size of a cocoa-nut, or that an acorn should produce a lofty oak. The phenomenon of growth, whether
* Eclectic Review, Third Series, Vol. IV. p. 37. (July 1830.)
more or less rapid, is altogether an admirable mystery, forming one of the broad distinctions between the works of nature and those of imitative art. Man can form nothing capable of altering its own structure by the process of assimilation which produces growth. A single blade of grass surpasses all the productions of human skill.
Owing to this rapid growth of the worm, had its original skin been the only one assigned to it, to serve for its whole caterpillar life, it would with difficulty have distended itself sufficiently to keep pace with the increase of its length and weight. Five times, therefore, in the course of its brief existence, it undergoes the process of moulting, casting off not only the whole covering of its body, but that of the feet, the entire skull, and even the jaws, including the teeth. These several parts may be discerned by the unassisted eye, but become very apparent when viewed through a lens of moderate power. In this process, a remarkable analogy may be observed to what takes place in the vegetable world.
• The buds of plants are composed of successive leaves closely embosomed within each other's foldings, the outer one being generally hard and corneous, from the exposure of its vessels to the colds of winter, while the inner leaves, being thence protected, remain soft and pulpy. But, as soon as the inner leaves receive an accession of sap, which rises from the roots on the return of spring, their vessels swell, and their nervures expand; while the outer leaf, from its vessels being shrunk and partly obliterated, undergoes little change besides being pushed out and sometimes entirely thrown off by the growth of the inner leaves which it had previously enclosed. On comparing one of the bud-envelopes thus thrown off, we can scarcely persuade ourselves that so small a covering could ever have contained the large spreading leaves which have burst from them.
• A caterpillar corresponds in several circumstances to the leaf-bud. The outer skin encloses a succession of several other skins, each becoming more delicate, soft, and indistinct than the one exterior to it; but gradually, like the expanding leaves, growing more substantial and firm as receives a supply of nutriment. The chief mechanical difference between the leaves folded up in the bud, and the successive caterpillars enveloped within the skin of one newly hatched, is, that the leaves in the bud receive all their nourishment through their footstalks from the root of the tree, whereas the caterpillar is nourished from within by the food digested in its stomach. The superfluous nourishment, usually in considerable quantity, and called the fat of the caterpillar, appears to lie between the successive skins, in a similar way to the adhesive gluten in the leaf-bud. But, as the first inner skin expands and increases in consistence, the fat which lies between it and the outer skin, seems to be absorbed into the body of the caterpillar, and of course swelling it out; while its abstraction from the interior of the outer skin renders this much more dry, separates it from
the inner skin, and disposes it to harden and shrivel. * The absorption of the fat also produces the remarkable consequence of gorging all the channels of nutrition, so that there is no longer any demand upon the stomach for fresh supplies of food. The caterpillar accordingly ceases to eat, and, having no incentive to action, remains motionless. The outer skin, meanwhile, being deprived of its internal moisture by the absorption of the fat, goes on to harden and shrink, while all the internal organs become enlarged by the nutritive fat. The expansion, therefore, of the body of the caterpillar on the one hand, and the shrinking of the old skin on the other, produce a mutual struggle, which, from the continued operation of the causes, must, it is obvious, be soon brought to a termination.
• The skin, from losing its internal moisture, loses also a portion of its colour, and becomes obscure and dull; and the caterpillar, from being girt and squeezed by its pressure, begins to turn and twist itself in various directions, to rid itself, if possible, of the inconvenience. By continuing these movements, the creature succeeds at length in rending the old skin at its weakest part, which is usually on the back, just behind the head ; and in a few minutes, using its body as a wedge,
l it may be seen issuing through the breach. The old skin is thus abandoned like a worn shirt; and the caterpillar appears in an entire new dress, the tints of which are fresher and brighter, and the colours and markings often considerably different from the former. The insect, also, in consequence of the quantity of fat which has gone to augment its several parts, becomes all at once so much enlarged in size, that we can with difficulty conceive how it could have been contained in the old skin out of which it has crept. The cast skin is frequently so very perfect, that it might almost be supposed to be the caterpillar itself, particularly in those which are hairy, as this contributes to the shrivelling. Ins. Transf. pp. 167–170.
This moulting of caterpillars, which, in some species, takes place as many as ten times, bears some slight resemblance to the casting of the feathers in birds, and the shedding of the hairy coat in quadrupeds. But, in these cases, the process is gradual and more superficial; the removing of the worn materials of the animal structure being chiefly effected by the absorbent system, which, in caterpillars, appears to be wanting. The successive changes of the skin accomplish all that is necessary in this respect: the hardening of the outer skin, which renders it less capable of distending so as to accommodate itself to the very rapid growth of the worm, seems to be necessary, that it may sufficiently answer the purpose of a sheath to
* Some writers have supposed that this fat is 'a sort of humour thrown off by the worm, to facilitate the moulting, which, spreading between the body and the skin about to be abandoned, lubricates their surfaces, and causes them to separate more readily.' (Lardner's Cyclop. Silk Manuf. p. 108.) But this representation does not account for the enlargement of the worm.
the tender and pulpy body, which is still further protected by the glutinous secretion or fat. It is probable, too, that the absorption of this fat produces a thickening of the inner skin, preparatory to its becoming the outer covering.
At length, the silk-worm has attained its full growth, and is a slender caterpillar from two and a half to three inches in length. During about ten days from its fourth moulting, it devours its food most voraciously; but, on attaining its full dimensions, its desire for food begins to abate, and it soon ceases even to touch the leaves. It now appears restless, erecting its head, and moving from side to side in quest of a place where it may commence its labour of spinning. In twenty-four hours from the time of its abstaining from food, the material for forming its silk will be digested in its reservoirs; its green colour will disappear; and before it is quite prepared to spin, its body will have acquired a degree of glossiness and greater firmness at the expense of some diminution of size. We transcribe from the Treatise on Silk in the Cabinet Cyclopædia, (reviewed in our last Number, the account of the subsequent process.
• The substance of which the silk is composed, is secreted, in the form of a fine yellow transparent gum, in two separate vessels of slender dimensions, which are wound, as it were, on two spindles in the stomach: if unfolded, these vessels would be about ten inches in length. When the worm has fixed upon some angle or hollow place, whose dimensions agree with the size of its intended silken ball or cocoon, it begins its labour by spinning thin and irregular threads, which are intended to support its future dwelling. During the first day, the insect forms upon these a loose structure of an oval shape, which is called floss sisk, and within which covering, in the three following days, it forms the firm and consistent yellow ball; the labourer, of course, always remaining on the inside of the sphere which it is forming
The silky material, which, when drawn out, appears to be one thread, is composed of two fibres, extracted through two minute orifices just below the jaw; and these fibres are brought together by means of two hooks placed within the silk-worm's mouth for the purpose. The worm, in spinning, rests on its lower extremity throughout the operation, and employs its mouth and front legs in the task of directing and fastening the thread. The filament is not spun in regular concentric circles round the interior surface of the ball, but in spots, going backwards and forwards with a sort of wavy motion. This apparently irregular manner of proceeding is plainly perceptible when the silk is wound off the ball, which does not make more than one or two entire revolutions while ten or twelve yards of silk are being transferred to the reel. At the end of the third or fourth day, the worm will have completed its task, and formed its cocoon.'
Lardner's Cab. Cycl. Vol. XXII. pp. 111, 12.