Skeleton of a large Water Beetle, as seen from below. B, the head. DD, the prothorax. FF, the mesothorax. HH, the metathorax. a a, fore legs. e e, fore wings. ii, middle legs. o o, hind wings. u u, hind legs. y, antennæ.

CHAPTER I.

THE Physiology of Insects is the account of how they are made: there are in every animal four essential elements,matter, motion, sensation, and mind.

Matter is inert-it does not move by its own powers; it is tangible- the touch ascertains that it resists: matter in animals has various degrees of consistency; convenience, however, has suggested its division into solid and fluid.

Matter, chiefly in its solid form, is the element of which the systems of organs are composed; and organs are the instruments by which functions are performed: in all animals there are seven systems of organs to perform seven series of functions. The seven systems of organs and their respective functions are these:-bones, for support; muscles, for motion; air-tubes, for respiration; blood-vessels, for circulation; alimentary canal for digestion; nerves, for sensation; and the organs of the sexes, for reproduction. The fluids in insects are blood and various secretions: the blood is supplied by nutriment transmitted from the alimentary canal: the solid parts are renewed by secretions from the blood.

Motion, in the animal frame, is of two kinds; dominant motion, which acknowledges not the authority of the mind; for instance, circulation of the blood: and subservient motion, which operates only in accordance with the behests of mind.

Sensation is the ultimate power of matter so perfected as to take cognizance of facts beyond the limits of the body: sensation is of two kinds; that derived from external objects, which appears the aim of animal life, and conduces to its maintenance, and that which conveys information from matter to mind, and behest from mind to matter.

Mind is the commanding element; the other elements in acting obey it, but in existence and characters are independent of it: no powers of mind can prevent the existence, or change the characters of matter, motion, or sensation: mind argues, then commands; it takes cognizance of causes, and provides for consequent effects, before the other elements can obey its behests. The great powers of mind are speculation and retention: speculation is the power which supposes an event that has not yet occurred;

and retention is the power of preserving an image left on the mind by an event that has occurred. Of the connexion of mind with the organs which it commands we know nothing; mind itself is only known by its effects: its commands are carried by the nerves; a fact ascertained by separating a nerve; after which separation, the mind no longer controls the parts to which that nerve extended its branches.

The physiology of insects is, however, properly confined to the description of their systems of organs, and to the functions which these organs perform: therefore, excepting as connected with the organs, no further notice will be taken of any other element than matter.

With regard to the anatomical nomenclature employed in the following pages, it will be, perhaps, advisable to make one or two observations. The author has studiously guarded against the admission of those terms which are of recent date, and seem invented without any other object than that of caprice: in every instance he goes back to the earliest name of which the meaning is clearly defined: he has invented no name except for parts which he found totally nameless. The authorities for the nomenclature of the external or osseous parts of insects, are Fabricius, Savigny, Audouin, and Straus-Durckheim. The labours of Fabricius and Savigny have been noticed with tolerable accuracy in Kirby and Spence's 'Introduction to Entomology'; those of Audouin with more skill by Mr. MacLeay, in the 'Zoological Journal'; and those of Straus by Mr. Doubleday, in the 'Entomological Magazine.' The author of this work has attempted to build a uniform anatomical nomenclature on his own observations, seeking amid these learned authors for the prior name given to each part: a portion of the result was published in the 'Entomological Magazine' under the title of Osteology of Insects, but the subject not being adapted to the taste of

the Entomologists of this country, it was abandoned. The terms now used are in accordance with those employed in the essay in question.

The chapter terminating the history of insects, and treating of their transformations, may perhaps be more strictly applicable to the present branch of the subject; but the author trusts that those graver and more scientific pages will serve, in some measure, to explain the changes previously described, and lead the enquiring mind to seek further information on the highly interesting subject of insect physiology. In the chapter in question it has been explained that insects, instead of an internal framework of bones supporting the softer parts, have their external skin or covering indurated, incrassated, ossified, invested with powers possessed by a skeleton or framework of bones, and fulfilling the very offices for which such a framework is designed, namely, supporting the softer parts, and affording points of attachment for the muscles. This indurated skin envelopes the animal in the manner of a suit of armour, enclosing and protecting from injury those parts which are softer and more immediately connected with vitality: in its composition this skeleton possesses more or less of the elements found in the bones of vertebrated animals.

In order to admit of perfect freedom in the performance of those numerous acts in which an insect's life is passed, it is essential that this bony covering should be possessed of the power of turning to the right or left, upwards or downwards; otherwise constant difficulty must occur. To accomplish this, the body, which is very long in proportion to its breadth, is divided into thirteen segments, the interstices between these being filled up by a softer and more flexible portion of the same skin. This division of the body into segments is exhibited very clearly in the earlier

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stages of an insect's life, and we see it much more distinctly in a larva than in a perfect insect; and here it will be proper to observe, that the skin or covering which has subsequently to become so corneous and solid that the term skin seems almost theoretical, is generally in larvæ, thin, soft and flexible, in an equal degree with that of animals possessing the more obvious support of an internal skeleton. The figure in the margin is intended to show the segments in the larva of a large beetle, each separated from its neighbours in order that the division may be more clearly Q exemplified. In the caterpillar of the emperor moth, at page 130, the same segmental division is equally manifest, with the exception that the segments are there represented united, as in a wstate of nature. The caterpillar of the spurge y hawk-moth, at page 90, is another exemplification of the same structure, the divisions being less manifest, but still to be traced; the thirteenth segment, or that posterior to the horn, being the only one not distinctly defined. See also the larva of the cricket, at page 73; of the sexton beetle, at page 53; of the bee, at page 40, &c. In examining larvæ, the young entomologist should pay particular attention to certain prehensile appendages erroneously called legs, and more correctly false legs: the absence, presence, number and situation of these, has been so correctly observed by entomological writers, that the genus of a moth or saw-fly may frequently be correctly given by a careful inspection of its larva. In the figure of the privet hawk-moth, at page 82, these false legs alone are used to hold it to the twig on which it is standing, the six real legs being unemployed: this is the usual and natural position of the insect when at rest: when eating

Elater.