Read Ebook: An Introduction to Entomology: Vol. 3 or Elements of the Natural History of the Insects by Kirby William Spence William

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Letter. Page.

It being judged expedient, since the publication of the last Edition of the first and second Volumes of this Work, to adopt a new plan with respect to the reference letters of the Plates, the Reader is requested to make the following corrections in those Volumes.

Page. Note.

INTRODUCTION

ENTOMOLOGY.

This system he has represented by tables of circles inscribed with the five primary divisions of each group. His first table exhibits a general view of organized matter as distributed in the animal and vegetable kingdoms--Thus:

Our learned author here divides the animal kingdom into what may be denominated five sub-kingdoms or provinces, in three of which no circulation of blood is visible, but which obtains in the rest. These he names--

His next set of circles shows the sub-division of these five sub-kingdoms into classes--Thus:

Sub-kingdom ANNULATA Cuv.

But there is another view of this subject before alluded to, which may be repeated here, and which seems to prove that the types of form in one natural group or class are reproduced in another; this appears to result from the following parallel series:

Psocus Hexapoda Galeodes Larunda.

FOOTNOTES:

?? ?? ??????? ????? ?? ???????? ???? ??????.

CLASSES.

EGG STATE.

I shall first give you a short abstract of the new hypothesis.

There being, therefore, this general analogy in their progress to that state in which they can continue their species between every part of animated nature, it holds good, I think, that the same analogy should take place in their developments. If the adult man or quadruped, &c. is evidently an evolution of the foetus, as from microscopical observations it appears that they are, if the teeth, horns, and other parts, &c. to be acquired in his progress to that state are already in him in their embryos, we may also conclude that the butterfly and its organs, &c. are all in the newly-hatched caterpillar. Again, if the blossom and its envelopes are contained in the gemma, the bulb, &c. where they have been discovered, it follows analogically that the butterfly and its integuments all preexist in its forerunner.

Perhaps after this view of the objections to Dr. Herold's hypothesis, it will not be necessary to say much with regard to the argument he draws from the change of organs--the loss of some and the acquisition of others--since this may readily be conceived to be the natural consequence of the vital forces tending more and more to the formation of the butterfly, and the withdrawing of their action more and more from the caterpillar; I shall not, therefore, enter further into the question, especially since the change of organs will come more regularly under our notice upon a future occasion.

Insects, therefore, as to their mode of birth, may be divided into--

Our business for the remainder of this letter will be with the latter description of these little animals.

I shall next amuse you with a few instances, in which the Allwise Creator instructs the parent insect, instead of defending her eggs with a covering furnished by her internal organs, to provide it from without, either from her own body or from some other substance. Most commonly, indeed, the female leaves her cluster of eggs without any other covering than the varnish with which in this case they are usually besmeared. Either they are deposited in summer and will soon be hatched, or they are of a substance calculated to encounter and resist the severities of the season. But many species, whose eggs are more tender or have to resist the cold and wet of winter, defend them in the most ingenious manner with a clothing of different kinds of substance.

A procedure nearly similar was observed by De Geer in some species of Aphides , which covered their eggs with a white cottony down detached from their belly by means of their hind legs. In this case, however, the eggs were separately coated with the down, but there was no general covering to the group.

It is probable that most of the above coverings serve another purpose besides the protection of the eggs from wet and cold--that of sheltering them from the action of too great light, which, as Dr. Michellotti by numerous experiments has ascertained, is fatal to the included germe. On this account it is perhaps that so many insects fasten their eggs to the under side of leaves. Those exposed in full day have usually an opaque and horny texture.

Frequently the whole number of eggs laid by one female is placed in one large group, more commonly, however, in several smaller ones, either at a distance from each other on the same plant, or on distinct plants. The object in the latter case seems to be, in some instances, to avoid crowding too many guests at one table, in others to protect the unhatched eggs from the voracity of the larvae first excluded, which would often devour them if in their immediate neighbourhood.

In the disposition of the eggs which compose these groups much diversity prevails. Sometimes they are placed without order in a confused mass: more frequently, however, they are arranged in different, and often in very beautiful modes. The common cabbage-butterfly and many other insects place theirs upon one end, side by side, so as, comparing small things with great, to resemble a close column of soldiers, in consequence of which those larvae which, on hatching, proceed from the upper end, cannot disturb the adjoining eggs. Many indeed have a conformation purposely adapted to this position, as the hemisphaerical eggs of the puss-moth , which have the base by which they are gummed membranous and transparent, while the rest is corneous and opaque. The same ready exit to the larva is provided for in the oblong eggs of the emperor moth , which are piled on their sides in two or more lines like bottles of wine in a bin.

Where the larva does not emerge exactly from the end of the egg other arrangements take place. The whirlwig-beetle and the saw-fly of the gooseberry &c. dispose theirs end to end in several rows; the former upon the leaf of some aquatic grass, the rows being parallel, the latter gummed to the main nerves of gooseberry or currant leaves, the direction of which they follow.

But the lackey-moths adopt a different procedure. As their eggs, which are laid in the autumn, are not to be hatched until the spring, the female does not, like most other moths, place them upon a leaf, with which they might be blown by the winter's storms far from their destined food, but upon the twig of some tree, round which she ranges them in numerous circles. If you examine your fruit-trees, you can scarcely fail to find upon the young twigs collections of these eggs, which are disposed with such admirable art, that you would take them rather for pearls, set by the skilful hand of a jeweller, than for the eggs of an insect. Each of these bracelets, as the French gardeners aptly call them, is composed of from 200 to 300 pyramidal eggs with flattened tops, having their axes perpendicular to the circumference of the twig to which they are fastened, surrounding it in a series of from fifteen to seventeen close spiral circles, and having their interstices filled up with a tenacious brown gum, which, while it secures them alike from the wintry blast and the attack of voracious insects, serves as a foil to the white enamel of the eggs that it encompasses. It is not easy to conceive how these moths contrive to accomplish so accurately with their tail and hind feet an arrangement which would require nicety from the hands of an artist; nor could Reaumur, with all his efforts and by any contrivance, satisfy himself upon this head. He bred numbers of the fly from the egg, and supplied the females after impregnation with appropriate twigs; but these, as though resolved that imprisonment should not force from them the secret of their art, laid their eggs at random, and made no attempt to place them symmetrically.

This boat, which floats upon the surface of the water until the larvae are disclosed, is placed there by the female gnat. But how? Her eggs, as in other insects, are extruded one by one. They are so small at the base in proportion to their length that it would be difficult to make them stand singly upright on a solid surface, much more on the water. How then does the gnat contrive to support the first egg perpendicularly until she has glued another to it--these two until she has fixed a third, and so on until a sufficient number is fastened together to form a base capable of sustaining them in their perpendicular position? This is her process. She fixes her four anterior legs upon a piece of leaf, or a blade of grass, and projects her tail over the water. She then crosses her two hind legs, and in the inner angle which they form, retains and supports the first laid egg, as it proceeds from the anus. In like manner she also supports the second, third, &c., all of which adhere to each other by means of their glutinous coating, until she feels that a sufficient number are united to give a stable base to her little bark; she then uncrosses her legs, and merely employs them to retain the mass until it is of the required size and shape, when she flies away, and leaves it to its fate floating upon the water.

A similar labour in providing suitable habitations for their eggs is undergone by various other insects whose larvae live chiefly on vegetable food, some inserting their egg within the substance the larva devours, as those that prey on timber, twigs, roots, or the like, and others on its surface. One would suppose at first, that the exceedingly small egg which produces the subcutaneous larvae would, by the parent moth, be imbedded in the substance of the leaf which is to exhibit hereafter their serpentine galleries: but this is not the case, for she merely glues it on the outside; at least such was the situation of the only egg of these very minute moths Reaumur had ever an opportunity to observe.

Within this integument is included a fluid, on the precise nature of which, except that it is an aqueous whitish fluid, few or no observations have been made, or indeed are practicable; but it is reasonable to suppose, that like the white and yolk of the bird's egg, it serves for the development of the organs of the germe of the future insect.

Another peculiarity connected with the present head is the augmentation in bulk which takes place, after exclusion, in the eggs of the great tribe of saw-flies , the gall-flies , the ants and the water-mites . Those of the two former, which are usually deposited in the parenchymous substance of the leaves, or of the young twigs, of various plants, imbibe nutriment in some unknown manner, through their membranous skins, from the vegetable juices which surround them, and when they have attained their full size are nearly twice as large as when first laid. Except in the eggs of fishes, whose volume in like manner is said to augment previously to the extrusion of the young, there is nothing analogous to this singular fact in any other of the oviparous tribes of animals, the eggs of which have always attained their full size when they are laid.

Some eggs after exclusion occasionally become slightly corrugated: Malpighi supposed that this occurs only when the eggs are barren, having observed that those of the moth of the silk-worm which preserved their plumpness always produced caterpillars, while those which lost their original rotundity and became wrinkled were constantly unprolific. Bonnet, however, found exactly the reverse take place in another moth, so that these appearances are scarcely to be depended upon. Kuhn asserts, that a virgin female of the puss-moth having begun to lay eggs, which were yellow above, green below, and depressed, he introduced to her an hour afterwards a male, and some minutes subsequently to the union, she again deposited eggs, which were wholly of a dark brown and convex.

With these exceptions, the eggs of all insects are hatched by atmospheric heat alone, the variations in which determine the more speedy or more tardy disclosure of the included insect. The eggs of such species as have several broods in the year, as the nettle butterfly when laid in summer are hatched in a few days; but if not laid till the close of autumn, they remain dormant through the winter, and are only hatched at the return of spring. That this difference is to be attributed to the influence of heat has been often proved by experiment: the autumnal eggs if brought into a warm room may be hatched as soon as those laid in the height of summer. Silk-worms' eggs naturally are not hatched till they have been laid six weeks, but in countries where they are reared, the women effect their exclusion in a much shorter period by carrying them in their bosoms: yet to retard their hatching with particular views is in many circumstances impossible. When the heat of the atmosphere has reached a certain point, the hatching cannot be retarded by cellars; and M. Faujas has remarked, that in June the silk-worm's eggs would hatch in an ice-house.

Some eggs change considerably both their form and consistence previously to being hatched. M. P. Huber found that those of different species of ants when newly laid are cylindrical, opaque, and of a milky white; but just before hatching their extremities are arched, and they become transparent with only a single opaque whitish point, cloud, or zone, in their interior. An analogous change takes place in the eggs of many spiders, which just before hatching exhibit a change of form corresponding with that which the included spider receives when its parts begin to be developed, the thin and flexible skin of the egg moulding itself to the body it incloses.

FOOTNOTES:

? xiv.

Reaum. iv. 425--.

De Geer i. 494--.

Reaum. vi. 434.

Reaum. ii. 401.

De Geer i. 192.

Ibid. ii. 982.

Reaum. ii. 97. 159.

De Geer iii. 48. 51.

Reaum. v. 122.

Ibid. iii. 197.

Reaum. iii. 8--.

De Geer vii. 194.

The sturgeon is said to lay 1,500,000 eggs, and the cod-fish 9,000,000.

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