its different transformations. These tubercles are known by the name of galls, and are very different in their form, texture, colour, and size. Galls of every kind, however, derive their origin from the stings of insects, which generally belong to the class of flies. The female fly, by means of her sting, makes incisions in the leaves or branches of a tree, and in each incision she lays an egg. This egg is at first cxtremely minute; but it soon acquires a considerable bulk, and the gall has arrived at its full size before the worm is hatched. This gall seems to be analogous to the membranes which invest a foetus, and expands in all directions in proportion to its growth. That the eggs of oviparous animals grow while in the ovarium is universally known; but it is singular that the eggs of gall-flies should grow after being separated from the body of the mother. These eggs must undoubtedly be furnished with external vessels, or a kind of roots, by which they extract juices from the internal cavity of the gall. Malpighi ascribes the origin of galls to a corrosive liquor introduced by the fly into the wound. But Reaumur, to account for the growth of a gall, thinks it unnecessary to have recourse to any supposed poisonous fluids, and attributes it to the superabundant nutritious juices derived to that particular part by the continual action of the absorbent vessels of the egg, joined to its heat, which may be compared to a little fire placed in the centre of the tumour.

I shall not inquire whether these causes are sufficient to explain the growth of galls. But, that the eggs deposited by the flies augment in size; that worms proceed fron them; that these worms are nourished, and live a certain time imprisoned in the galls; that they are there transformed into nymphs or chrysales; and, lastly, that they are metamorphosed into winged insects, which, by gnawing an aperture

through the gall, take their flight in the air; are known and incontestible facts. Examine the common oak-galls, or those of any other tree; if any of them happen to have no aperture, cut them gently open, and you are certain to find an egg, a worm, a chrysalis, or a fly; but in such as are perforated, not a vestige of an animal is discoverable.

Some caterpillars, when about to transform, make a belt pass round their bodies. This belt is composed of an assemblage of silken threads spun by themselves, the ends of which they paste to the twigs of bushes, or other places where they choose to attach their bodies. They likewise fix their hind legs in a tuft of silk. After transformation, the chrysales remain fixed in the same manner as before their metamorphosis. The belt is loose, and allows the chrysalis to perform its slow and feeble movements.

The whole moth-kind, as well as the silk-worm, immediately before their transformation into the chrysalis state, cover their bodies with a cod or clue of silk, though the nature of the silk, and their mode of spinning, are very different. The cod of the silk-worm is composed of pure silk, and produced by numberless circumlocutions and zigzags of the same thread. Their figure is generally oval, which necessarily results from that of the animal's body upon which they are moulded. When spinning, they twist their bodies into the form of an S. The silk is spun by an instrument situate near the mouth of the insect. The silky matter, before it is manufactured by the spinning instrument, appears under the form of a gum almost liquid, which is contained in two large reservoirs contorted like the intestines of larger animals, and which terminate at the spinning instrument by two parallel and slender conduits. Each conduit fur

nishes matter for one thread. The spinning instrument, as is evident when viewed by the microscope, unites the two threads into one. Thus a thread of silk, which has the appearance of being single, is in reality double, and spun with great dexterity. Some writers, who delight in the marvellous, ascribe foresight to the silk-worm in spinning its cod. The silk-worm, it must be acknowledged, acts as if it foresaw the approaching event. But the truth is, that, when the animal has acquired its full growth, its reservoirs of silk are completely filled. It then seems to be strongly stimulated to evacuate this glutinous matter. Its different movements and attitudes, while discharging the silk, produce those oval bundles which clothe and ornament vast numbers of the human species.

Another species of caterpillar constructs its cod in the form of a boat with the keel uppermost; but it consists not entirely of pure silk. The animal, with its teeth, detaches small triangular pieces of bark from a bush or tree. These pieces of bark it pastes upon its body by means of a glutinous or silky substance, and they constitute a principal part of its cod.

Another species works also in wood, though not with equal art as the former. Its cod is composed entirely of small irregular fragments of dried wood. These fragments the animal has the address to unite together, and to form of them a kind of box which covers and defends its whole body. It accomplishes this purpose by moistening, for some moments, the pieces of wood in its mouth, and then attaches them to each other by a glutinous substance. Of this mixture the caterpillar forms a cod, the solidity of which is nearly equal to that of wood.

The most solitary of all insects are those which live in the internal parts of fruits. Many of them undergo their metamorphosis in the fruit itself,

which affords them both nourishment and a safe retreat. They dig cavities in the fruit, which some of them either line with silk, or spin cods. Others leave the fruit, and retire to be transformed in the earth.

The metamorphosis of insects has been regarded as a sudden operation, because they often burst their shell or silky covering quickly, and immediately appear furnished with wings. But, by more attentive observation, it has been discovered, that the transformation of caterpillars is a gradual process from the moment the animals are hatched till they arrive at a state of perfection. Why, it may be asked, do caterpillars so frequently cast their skins? The new skin, and other organs, were lodged under the old ones, as in many tubes or cases, and the animal retires from these cases, because they have become too strait. The reality of these encasements has been demonstrated by a simple experiment. When about to molt or cast its skin, if the foremost legs of a caterpillar are cut off, the animal comes out of the old skin deprived of these legs. From this fact, Reaumur conjectured, that the chrysalis might be thus encased, and concealed under the last skin of the caterpillar. He discovered that the chrysalis, or rather the butterfly itself, was inclosed in the body of the caterpillar. The proboscis, the antennæ, the limbs, and the wings of the fly, are so nicely folded up, that they occupy a small space only under the first two rings of the caterpillar. In the first six limbs of the caterpillar are encased the six limbs of the butterfly. Even the eggs of the butterfly have been discovered in the caterpillar long before its transformation.

From these facts it appears, that the transformation of insects is on the throwing off external and temporary co d not an alteration of

the original form. Caterpillars may be considered as analogous to the foetuses of men and of quadrupeds. They live and receive nourishment in envelopes till they acquire such a degree of perfection as enables them to support the situation to which they are ultimately destined by Nature'.

No. XXXVI.

ON TRANSFORMATION IN GENERAL.

Omnia transformant sese in miracula rerum.

VIRGIL.

From form to form they pass in wondrous change.

The transformation of caterpillars into winged insects has long excited our admiration. But transformation is not confined to them: all animals, without exception, undergo changes in their structure, mode of existence, and external appearances. Mankind, from their embryo state to their final dissolution, assume many different forms. With respect to an infant, immediately after birth, it is observable to all, that its form, its symmetry, and its organs, are by no means complete. The head, for some time, is disproportionally large; the hands and feet are not properly shaped; the hair is short and scanty; and no teeth appear. In a few months, however the symmetry of all the parts is evidently improved, and the teeth begin to

For more on this subject, consult Lesser's InsectoTheology, by Lyonet, Svo. Lond. 1799, a highly curious and interesting work.