The INOPERCULATA, or typical Pulmonifera, are naturally divided into the slugs, land snails, and water snails; and are embraced in the following families:

S Animal slug-like

2.

وو

...

contained in a more or less spiral shell

Mantle small, shield-like

enveloping the body...

2

3

Limacide

...

Oncidiada

...

...

...

4.

(Animal aquatic, aperture of shell edentulous, Limnaida

Aperture of shell toothed

SLUGS (FAMILY LIMACIDE).

Auriculida

Slugs are very conspicuous among the mollusca, and readily recognized by their elongated, more or less naked bodies. The body is united in its whole length with the foot beneath; the head is furnished with four cylindrical tentacles, and eyes are situated on the upper pair. . The slugs resemble in many respects the snails, and are regarded by the vulgar as such, which have the peculiar power of leaving their shells during the summer and retiring to them again for protection on the approach of winter; so that, if this were true, we ought only to find snails during one season and slugs during another. But the snail cannot leave its shell, being attached to it by muscles. There are many points of difference

between these two familiar animals. Firstly, one afforded by the nature and position of the shell. Observe the oval prominence on the back of that large spotted slug (Limax maximus); this is the mantle which in the snail forms a sack through which the head and foot protrude, but in the slug covers but a small part of the body. Beneath the shield-like mantle lies a thin shelly plate which protects the viscera. A snail may be viewed in the light of a slug whose visceral matter and mantle are elongated upwards, and then spirally coiled, the mantle secreting an external shell, instead of depositing shelly matter from its inner surface. The shelly plate of the slugs has been called the snail's stone, and was formerly esteemed a valuable medicine in cases of gravel and strangury. This internal shell varies in size, structure, and position in the different species and genera, a fact overlooked by Swammerdam; for to account for large slugs having "very small membranous plates, while the smaller ones had them often much larger, and formed of solid stone," he was inclined to think "that the snails change this their little stone yearly, in the same manner as crawfish change those two semiconvex and plain stones which are likewise placed in their thorax, and are improperly called crab's eyes." Beneath the mantle on the right side of the

body is an aperture leading into the respiratory orifice.

The lingual ribbon of the slugs is characterized by its numerous transverse rows, containing a large number of very similar teeth; in general, the central tooth has a long central point with a small denticulation on each side of it; the lateral teeth, as they approach the margin, become spine-like, having but a long projecting point.

All molluscous animals excrete a mucous fluid to lubricate the skin, furnished by glands situated in it; the slugs copiously exude this slime, more especially when irritated. The "silvery slimy trails" of slugs and snails are depositions of mucus left in their tracks. The slugs are divided into four genera, characterized principally by the relative positions of the mantle, shell, and respiratory orifice. Thus in Arion the shell is represented by mere calcareous granules in the mantle ; the respiratory orifice is near the fore part of the shield; the body is truncated behind, and terminated by a mucous gland. In Limax the shell is of the nature of a thin oblong, or slightly concave plate, the mantle-shield marked with concentric lines, and the respiratory orifice near the hind part of the shield. Geomalacus has a gland at the extremity of the tail like Arion, the respiratory orifice nearer the front than in Limax,

and the internal shell claw-shaped. In Testacella we have a near approach to the snails, and through Vitrina is connected with them; the shell is small, ear-shaped, placed externally at the hinder extremity of the body, and covers the mantle, beneath which, on the right side, is the respiratory orifice.

GENUS ARION.

Arion was a horse remarkable for its speed, but our Arion is remarkably slow.

ARION ATER-(the Black Slug) (Pl. V., fig. 31)— is familiar to all as a common object of our gardens and waysides, and is also too well known to the gardener, as being more or less injurious to the early cabbages and other garden produce; and in the autumn as one among other mollusks that mutilate and render repulsive the fruits of that season. Dead animal matter-even that of their own species-does not come amiss to them; they also feed on the common earth

worm.

The adult animal is usually brownish or greyish-black; at other times brown or reddish; the young individuals are grey, whitish, bluish-white, or yellow-coloured. It attains a length of from three to five inches. The shell is composed of loosely aggregated calcareous particles.

Cuvier writes, that "the finest injections do not produce anything more agreeable to the eye of the anatomist than the white ramifications of the arteries in the black slug." The arteries are opaque and milk-white, and strongly contrast with the dark grounds upon which they trace their course; as, for example, the dark green of the intestines, or the blackish-brown of the liver. The heart is included in a very thin bag, or pericardium, in the cavity of which there is abundance of a watery fluid, as clear as crystal.

Arion ater frequents damp and shady woods and thickets, gardens, and hedge-banks; during the day it is never seen abroad, except after rain, retiring under stones and logs of timber, or burying itself in the earth; for the dry atmosphere would deprive the body of its moisture, so essential to the existence of the animal.

It deposits its globular, semi-transparent eggs in May, among the roots of plants. This slug, as also some other of the larger species, is infested by a small yellowish-white mite, Philodromus limacum of Jenyns, who has given a very interesting account of the habits of the little animal. The parasites may be seen running in some numbers over the body of the slug. It is curious that the slimy surface of the slug's back does not impede the progress of these