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Indian species, which forms a beautiful network, strengthened by a branching system of ribs, like the ribs and fibres of a skeleton leaf. Four British species of Gorgonia, one of them common on the Devonshire coast, are recorded. G. verrucosa, the commonest of these, is from six to twelve inches high, and much branched, like a tree; but its branches do not form a network. Its coral has a dense, black axis, of a horny substance, which encloses a white pith, and is coated with a whitish crust, covered with warts, arranged in somewhat spiral lines. Such is the aspect of the dried polypidom. When living the crust is soft and flesh-coloured. The Alcyonium, another member of this order, has already been noticed. More interesting and beautiful forms are found in the family of Pennatulidæ or Sea-pens, of which three species, arranged under as many genera, are natives of Britain. These curious animals present us with the fact of compound bodies, in all respects analogous to corals, existing in an unattached state, (that is, not rooted or fixed to any base, but freely planted in soft mud,) and possibly capable of a motion through the water from place to place. The fact of this motion has been asserted by several naturalists, but observations are wanting in corroboration. The Sea-pen itself (Pennatula phosphorea) is one of the most singular and beautiful of the British Zoophytes. The polypidom is three or four inches in length, fleshy, of a purplish-red colour, narrow and naked at the lower end, and feathered on its upper half with long, closely-set pinnæ, along the margins of which the polype-cells are placed. These pinnæ are obliquely curved backwards, and capable of

152

VIRGULARIA MIRABILIS.

separate or united motion; and they have been supposed,

VIRGULARIA MIRABILIS

by authors who believe in the

[graphic]

swimming powers of this zoophyte, to have the regular oar-like motion of fins. Through the centre of the stalk runs a calcareous column, which serves to stiffen the body of the polypidom. When irritated, this zoophyte is brilliantly phosphorescent; but it does not emit light unless disturbed, or under the influence of pain. Professor Forbes has remarked that, when it is touched, the luminosity commences at the point of contact, and proceeds upwards to the polypiferous portion of the zoophyte, but never in a contrary direction; and when the centre of the polypiferous portion is struck, the polypes below the injury are not affected, while those above it emit light. "When thrown into fresh water, the Pennatula scatters sparks about in all directions, -a most beautiful sight." The

STRUCTURE OF POLYPIDOM AND POLYPES. 153

Virgularia mirabilis is another of this family, closely allied to Pennatula, but of a much more slender form, resembling a rod, whence its name. It is several inches long and quite straight, traversed by a cylindrical calcareous stem or column, coated with a transparent flesh. Through nearly its whole length this rod-like body is furnished with short fin-like lobes of a crescent shape, which approach in pairs, but are not strictly opposite ;-they are about the eighth of an inch asunder, and are furnished along the margin with a row of urn-shaped polype-cells. These lobes have the power of contracting, so as to lie closely imbricated one on another; and of expanding to an angle of about 30°, so as to leave open spaces between. They are of a pale orange-fawn colour, gracefully curved backwards, and each contains about eight polype-cells. The polypes are objects of great beauty, and their form may be very well seen even after death; for, though capable of retractation within the cell, the tentacula have no contractile power, and may be made to expand in their full extension by merely pressing upon the cell. The polype thus displayed is an eight-rayed star, the rays curved backwards, channeled, and elegantly pectinated along each margin. In the centre is the mouth, with prominent lips. The Virgularia is found chiefly in Scotland and the north of Ireland, and I have taken it recently on the Galway coast in Birturbui Bay. The only remaining British Zoophyte of this group, Pavonaria quadrangularis, is exceedingly rare, and has yet been taken only near Oban, on the West of Scotland. In its form it bears a considerable resemblance to the Virgularia, but is curved, and of much greater dimensions,

154 INSECTS AND CRUSTACEA DISTINGUISHED.

the length being sometimes forty-eight inches. When irritated it emits a bluish light.

The great class of CRUSTACEA, of which Crabs and Lobsters are familiar examples, demands some notice, but is so varied in its aspect and in the numerous types which its orders, families, and genera present to us, that I cannot attempt to give, in the few pages to be devoted to the subject, even an outline sketch of its classification. I can scarcely do more than notice in this place a few of the commoner Crabs which one meets with in dredging.

The class Crustacea of modern authors was included by Linnæus among his Insects, and formed a part of the Aptera or wingless insects of that author. The structure of a Crab or Lobster, or a Woodlouse, which are all members of the class, does indeed in many ways resemble that of the true Insects. The body is cased with hard materials, it is divided by articulations into several rings, it is furnished with jointed legs and with those curious organs called antennæ or feelers, and it possesses a mouth constructed on a very similar type. There is one peculiarity, however, in which there is a remarkable difference between the Crustacea and both the Insect and Spider Classes. These latter groups of animals are destined to live in the air, and their respiration is consequently performed by lungs. Even such species of them as are aquatic carry with them under water the quantity of air necessary to their existence, just as a diver inflates his lungs before he leaves the surface; though it is quite true that some breathe through the medium of gills while they continue in a rudimentary state. The

GILLS OF CRUSTACEA.

155

Crustacea, being either water animals, or constantly frequenting very damp places, respire through the medium of gills. This is one important feature in their economy by which they differ from insects. Another is, that they continue to increase in bulk after they have attained the mature form of their kind. In the insect, increase in bulk, and the changes of skin which it requires, are confined to the metamorphic stages through which the animal passes, and cease when the limbs acquire their permanent form. In the Crustacean, though the earlier stages undergo metamorphoses, some of them quite as singular as those that we find among insects, the animal continues to increase in size long after its limbs have been completely formed; and the provision by which this is effected is not the least curious point in their history. Differences of this important nature, and others of a similar kind, added to the immense extent of both classes, have induced modern naturalists to separate the class Crustacea from the other articulate animals with which Linnæus combined them.

The different aspects which the gills assume in the various groups of Crustacean animals, while they afford, as in other classes, excellent classifying characters, exhibit to us some beautiful adaptations, which are quite as interesting to the unlettered observer as to the systematic naturalist. In some of the more minute individuals of the race, as in the Waterfleas, which may be found by myriads in any stagnant pool, the respiratory organs are seated in the legs themselves, whose covering is so delicate that it admits the vessels that ramify over

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