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THE INTELLECTUAL OBSERVER,
INSECTS' EGGS: THEIR STRUCTURE, VARIETY,
BY JABEZ HOGG, F.L.S., HON. SEC. R.M.S., ETC.
(With a Coloured Plate.)
IN our country rambles, some among us may have been tempted to examine what appeared to be curled-up leaves, or patches of whitish dots adhering to branch or stem, many so like the bark of the tree itself, that at a first glimpse, even the practised eye might have failed to detect that they were organised bodies. Upon more closely and attentively scrutinizing these little adhesions, they are seen to be collections of insects’ eggs, thus skilfully deposited and concealed with maternal care. To such apparently unimportant objects I would direct the reader's attention, and more particularly to their structure, variety, and beauty, as disclosed by the aid of the microscope. My observations will be mainly confined to the eggs of the Lepidopterous insects, which at this period of the year may be secured in large numbers, for the purpose of making a careful comparison of their formation, watching the development of the germinal vesicle into that of the fully-formed embryo, and noting the transformation of the creeping caterpillar to a thing of wondrous life and beauty, taking its flight among the loveliest of nature's handiworks, and sipping honey from every flower “from morn to dewy eve.”
Nearly all insects are oviparous; the few instances in which this is believed not to be the case, are not positive deviations from the general law. The eggs of insects, however, do not often fall under notice, for in consequence of their smallness, they escape observation; and from the scrupulous care taken by the parent to conceal them from the depredations of their numerous enemies, they are not easily discoverable. The situation mostly selected by the female moth, is the leaf or bark of such trees and plants as will serve their young for food. Sometimes, with an instrument provided by Nature for the
VOL. XII.-NO. V.
purpose, she bores a hole in the bark in which to deposit them. Not infrequently the interior of fruit or grain, or even a dung-heap is selected, and some few commit their store to water, there to await the heat of the summer sun to hatch the brood.
Their defence against cold, and atmospheric changes consist in coating the inside with a varnish-like substance, while the outside is often covered over with a denser material, as portions of vegetable fibre and the hairs or feathers from the body of the insect, which, together with the leaf on which the eggs are laid, form groups of tiny nests. Others form stronger and more durable receptacles. The female cock-roach constructs a strong horny bag, or purse, in which having deposited her eggs, she carefully carries it about with her. The coccus converts her whole body into a shield or covering for her eggs, so thoughtful does she appear for the future safety of her brood. As a general rule, the female insect having deposited her full number of eggs, leaves them to be hatched by the heat of the sun, which may be accomplished in a few days, or not until the following spring, as is the case with the eggs of the silkworm, and all those laid late in the summer or autumn. The number of eggs produced by different species is very varied, some depositing only two, while others, and by far the largest number, lay them by hundreds. The ant is said to lay from thirty to forty thousand in a year. The queen-bee, fifty thousand; but I believe the ordinary number is much below this. The silkworm moth mostly lays about five hun. dred eggs. The gcat-moth, about a thousand, and the tigermoth some fifteen hundred, arranged with the most uniform and symmetrical order. Insects' eggs bear great extremes of temperature without losing their vitality; want of air and light appear to be far more speedily detrimental in this respect than the extremes of heat or cold. I have exposed silkworm's eggs to severe frosts, and also plunged them into scaldingwater, without in the least affecting them, either for good or evil. Several genera of moths with wonderful instinct, cover their eggs with soft vegetable materials; and some, it is asserted, pluck the hair and feathers from their bodies for the same purpose. A writer states, I think, without sustaining the statement by sufficient evidence, that moths use a pair of pincers, placed at one extremity of the body, for plucking out their hairs to cover their eggs; but this would scarcely seem to be needful, since the eggs are nearly always deposited in groups, and securely fastened up in the leaf on which they have been deposited, so that frequently it requires some force to separate the bundle, and expose them to view.
Some of the Coleopterous insects resort to curious and inge