thin, dark-coloured membrane; the auricles open by contracted valvular orifices into two white strong tubes; these, united, form the ventricle, which terminates in an artery that goes to the boring-shell. The heart is loosely attached; its action is distinctly seen through the external covering, and in some instances continued to act after it was laid bare.

"The first contraction is in the two auricles, which are shortened in that action. This enlarges the ventricle before it contracts. The great artery from the ventricle goes directly to the head, and the vessels that supply the auricles are seen to come from the gills. The auricles are lined with a black pigment, so that their contents cannot be seen through their coats, and the ventricle, from its thickness, is not transparent; but the muscles of the boring-shells are of a bright red, and all the parts between the heart and head are supplied with red blood."

In the Teredo, then, every part of the blood "passes through the vessels of the gills, and then through the cavities of the heart. As this animal is to work a machine capable of boring a very hard substance, and to go on working during the whole of that period of life in which its growth is continued, to make room for the increased bulk, so it requires that the blood be more highly aërated, and supplied with greater velocity to these active organs. The heart, also, to give it greater advantage in these respects, is placed near to the boring-shells, so that the blood which goes to them is of the brightest colour.

"In this circulation, the first action of the heart is to supply the different parts of the body with aërated blood: upon this the activity of the heart is wholly exerted; the blood is returned more slowly through the gills, and remains there a longer time, so as to receive a greater degree of the influence from the air contained in the water." (Lectures on Comp. Anatomy, vol. iii. p. 162, 163.)

In the Mollusca tunicàta, the circulating apparatus is simpler than in any of the other orders. The heart of the Ascídia is an organ with a single cavity, situated near the stomach, and presents a less distinct muscular structure than it does in cephalous Mollúsca. It is of an oblong or spindle shape, and the two extremities are prolonged into two vessels, almost equal to itself in their diameter. One of these vessels receives, as it is believed, all the blood from the branchiæ, and is in consequence named the branchial vein; the other, of greater length, is an aorta to distribute the blood through the whole system. (Savigny, Mém. sur les Animaux sans Vertèbres, vol. ii. p. 113.)

Such is a very general outline of the circulation in this tribe; nor are the particular modifications to which it is subject, of sufficient interest to detain us. I may just remark, that the minute vessels of the branchiæ form a beautiful network, similar to that on the branchial leaves of bivalves.

The heart has been seen pulsating in several Mollúsca whose bodies possess a considerable degree of transparency. The pulsations are slow, and often at unequal intervals; but this irregularity may be the effect of weakness or of pain; for the animals must be placed in unnatural positions, or removed from their proper element, before the observations can be made; and an attention to this circumstance may explain the fact of a retrograde motion of the circulating fluid, which has been observed by some naturalists. The blood itself is of a bluish white colour, and glutinous consistence. Lister tells us, that when he kept the blood of a snail in a vessel for some days, it remained liquid and entire, not separating, in the manner of human blood, into two portions of unequal densities; but, when he applied heat, it readily congealed into an opaque bluish coagulum, just as the human serum would have done under the same circumstances. But Lister knew well that the blood of these creatures was not homogeneous; for he adds, that with a good microscope it is easily shown to consist of globules swimming in a limpid fluid; that these globules are truly round, and considerably exceed in size those of human blood; they are also heavier than the fluid part, since they gradually sink to the bottom when kept still in a glass tube. (Exercitatio Anat. de Cochleis, p. 95. Lond. 1694.) The late experiments of Prevost and Dumas have confirmed those of the old English naturalist: they have ascertained that the globules of the snail have a diameter one third greater than those of man and quadrupeds; and, what is more remarkable, they found the globules to be really spherical, as Lister has asserted, although analogy would have led us to a different conclusion; for they are elliptical in birds, reptiles, and fishes, to which the Mollúsca are certainly much more nearly allied than they are to the Mammàlia. (Zoological Journal, vol. i. p. 178.) The globules in the bivalved Mollusca

*The red globules of human blood, according to the observations of Mr. Bauer, as corrected by Kater and others, are one five-thousandth part of an inch in diameter. (Home's Comp. Anat., vol. iii. p. 4., compared with p. 12.) But in the fœtus, the globules, say Prevost and Dumas, differ in their form and volume from those of the adult; the former being double the size of the latter (Bostock's Physiology, vol. ii. p. 200.), and approximating nearer, of course, to the size of those of Mollúsca. The fact is curious, when considered in relation to some speculations of Carus.

are also, according to Poli, an eminent naturalist of Naples, much larger than in man; so that he considers the latter to be to the former as hemp-seed to millet-seed. (Rudolphi's Physiology, by How, vol. i. p. 132.) The red colour of blood has been attributed to the existence of iron in it in combination with phosphoric acid; but it militates against this hypothesis when we find that the white blood of the Mollúsca, although the contrary has been asserted, contains the same mineral ingredient: for Erman has detected iron, and very probably also manganese, in the blood of the Hèlix pomatia and Planórbis córneus; and Poli likewise speaks of iron in the blood of A'rca glycýmeris. (Rudolphi's Physiology, by How, vol. i. p.113.) As the following analysis may probably be applied with safety to the whole class, I extract the passage entire, notwithstanding it repeats some particulars already noticed:"The blood of the Hèlix pomàtia," says M. Gaspard, “is rather thick, but without viscosity; it has a faint smell, a slightly saline taste, and is so abundant that each individual contains not less than a drachm and a half. It is of a delicate blue colour, which is neither altered nor modified by change of aliment, by asphyxia, or by hybernation. It is miscible with water, but of greater specific gravity, and falls to the bottom in visible streaks or entire drops. When exposed to the atmosphere, it does not spontaneously congeal, like that of vertebrated animals, but it separates by rest into two distinct fluids: the one blue, which swims at the top; the other colourless and opaque, remaining at the bottom of the vessel. In a few days it decomposes with fetor [stench]. It is unaltered by muriate of barytes, and by alcohol; is simply discoloured by potash, and by vinegar and other weak acids: but acetate of lead, nitrate of silver, and, still more, nitrate of mercury, occasion a copious dense precipitate. Boiling water, sulphuric and nitric acid, coagulate it strongly, like albumen." (Zoological Journal, vol. i. p. 177.) I am, Sir, yours, &c.

Nov. 12. 1831.

G. J.

ART. VII. Illustrations in British Zoology. By GEORGE JOHNSTON, M.D., Fellow of the Royal College of Surgeons of Edinburgh.

Sir,

1. LUCERNA'RIA AURICULA.

I Do not think that the discovery of any new object or fact in natural history ever gave me greater pleasure than the first sight of the little creature here delineated. Its form is so

singular, and so far removed from any with which non-naturalists are familiar, that some of my friends, on seeing the drawing, have actually asked to which kingdom, animal or vegetable, the thing belonged; and to uncommonness of shape, in adds beauty in colour and in ornament, and much vivacity in its motions. There is, to my eye, not a more lovely object among the numerous interesting worms that dwell on our shores. I had, on a summer's evening, taken a favourite station by the side of a pellucid pool hewn by nature in the rock, and was admiring the mimic landscape reflected from the water, when my attention was caught by what seemed to be a clot of blood adhering to the frond of a sea-weed; it might be, was the passing thought, a small bit of the liver of some mutilated fish, when, lo! it moved, and suddenly expanded before me in all its beauty. It was impossible to restrain open expression of admiration and pleasing surprise. It had risen up like an enchanted thing, and in a shape so novel, that fancy had not imagined its existence among animated beings; it displayed its ornaments, the beads and tassels of its border, with such grace, and its rich colour contrasted so well with the sombre darkness of the weed on which it had settled, that the most apathetic would have been warmed; while I leaped for very joy, and said within myself, Surely the Creator of all holds this out to lure his rational creatures to study his works, and search out his wisdom!

Our figure (fig. 29.) is of the natural size, and the individual from which it was taken was of a clear pinkish red colour. It

29

adheres by a short stalk, which dilates into eight equal oblong arms, each terminated by a globose tuft of filaments, tipped with a gland. The arms are mottled with two rows of spots, produced by the opacity and configuration of the internal viscera; and they are connected together by a transparent membrane. Between each of them there is an oval vesicle placed on the edge of this membrane. Within the stalk there is a

tube, which, prolonged, seems to form the mouth, of a square shape, projecting in the centre of the arms.

Lucernaria aurícula can move about at will, but has apparently not much power for distant excursions, and little inclination to roam. Fixed by means of its stalk, which is presumed to act as a sucker, on the leaf of a sea-weed in some sheltered pool near the lowest tide-mark, it escapes its enemies, I know not how; for it is the most helpless of creatures, without weapons of offence or defence. It catches little animalcules brought within its reach by the tide or their own destiny; and, for this purpose, the tentacula are widely displayed, and no sooner have they felt the prey, than they instantly contract, envelope it in their joint embrace, and carry it to the mouth. Lamarck says, that the globules at the tips of the filaments or tentacula are suckers; and if the observation is correct, it is obvious that this structure must enable them to retain living prey with great additional obstinacy.

This Lucernària is, I believe, a rare animal on our coasts, of which it was first ascertained to be a native by Mr. Montagu, who took it on the coast of Devonshire, and gave a figure and description of it in the ninth volume of the Linnean Transactions. In the edition of Pennant's British Zoology published in 1812, there is an account of it borrowed from Montagu's paper, but erroneous in many respects. Dr. Fleming's description, in his history of British Animals, is, however, evidently original. He says, the species is found on different parts of the coast. The colour, according to him, is "brownish: " according to Montagu, it is variable; and this may, with proper limitation, be correct, for our specimen was of a fine transparent red. It was taken in Berwick Bay. Lucernària belongs to the class Radiàta, order Acalèpha Cuvier, Móllia of Lamarck.

Berwick-upon-Tweed, Nov. 10. 1831.

GEORGE JOHNSTON.

ART. VIII. On the Parasitical Connection of Lathræ'a Squamària, and the peculiar Structure of its subterranean Leaves. Read at the Linnean Society in November, 1829.

OUR readers will remember that in Vol. II. p. 105. Mr. Bowman, in noticing certain differences in habit and external organs which he had found to obtain in specimens of this interesting plant procured from, or observed in, various localities, incidentally announced his having discovered its true