312 Lignites of the Giant's Causeway and the Isle of Mull. which it dissolves with effervescence) the same constituents as the laminated variety.

In a comparison of the composition of the lignites of the Giant's Causeway and the two varieties of the Isle of Mull, it is necessary to take into consideration the large amount of ash afforded by the one form, from the latter locality, which has resulted from the mechanical intermixture of mineral with organic matter in the laminated variety. As the exact amount of matter in this ash of a mechanical origin cannot be known, a better comparison of the real percentage composition of organic matter will be obtained by deducting the ash in each The three analyses thus calculated exhibit the follow

case.

*

The foregoing analyses justify the conclusion of Bischoff, "that the composition of brown coal differs from that of ordinary coal, inasmuch as there is a smaller proportion of carbon, and a larger proportion of oxygen," in the former than in the latter, since we find that the Giant's Causeway specimen is not only more woody in its nature, but that it also possesses the true elements in such relative proportion as might be expected from the comparatively small amount of decomposition which this form has undergone. The change which converts woody fibre into coal, consisting principally in the evolutions of carbonic acid gas, by means of which the proportion of carbon and hydrogen become increased, and a substitute capable of yielding a greater amount of flame is usually produced.

* Chemical and Physical Geology, vol. i., p. 266.

313

Description of two Tubicolar Animals. By T. STRETHILL WRIGHT, M.D., F.R.C.P.E.* (Plate VII.)

In February last I received a number of Caryophylliæ from Ilfracombe, and, on examining one of these, I found three specimens of an animal, which I am led to believe is undescribed, inhabiting the stone to which the Lithophyte was attached.

The body of the largest specimen (fig. 1, Plate VII.), when fully extended, consisted of a hollow tube or tunic about ths of an inch in length by 13th of an inch in diameter, smooth, and bearing no trace of annulose structure. Its summit was crowned by an expansion of sixty undivided tentacles, similar to those of a Polyzoan mollusc, and clothed with cilia, the motion of which presented the usual appearance of teeth moving in opposite directions on opposite sides of the tentacles. The tentacles were united at their base by a thick membrane, and were arranged in a crescent as in Polyzoa of the Hippocrepian type. The concavity of the crescent dipped downwards, and consisted of shorter tentacles, as in Plumatella.

The animal inhabited a transparent tube or cell of membranous texture, the mouth only of which could be detected, as the rest of the tube was deeply buried in the stone. Although it was frequently found extended in a remarkable degree from its cell, the slightest shock caused it to retract itself and disappear with a quick jerk within its retreat. As its posterior extremity, therefore, was never visible, it was only possible to examine part of its anatomical structure. This consisted of the alimentary system, the vascular system, the muscular system, and the integument.

The alimentary system consisted, as in Plumatella, of a mouth placed within the tentacular cup, and closed by a semilunar lip or valve. The mouth opened into a long tube or gullet, which passed down the axis of the body and disappeared within the cell of the animal. The alimentary canal probably communicated there with a stomach, and then

* Communicated to the Royal Physical Society of Edinburgh, April 1856.

returned upwards to the mouth of the cell, where it again became visible as a thin membranous tube passing up the body, and terminating, as in Plumatella, in an anal orifice, situated immediately beneath the tentacular crown on its concave aspect. The mouth was generally in constant motion; and when the animal was undisturbed, ciliary action and the passage of nutritive matter were detected within the interior of the gullet, while the ejection of the peculiar fusiform fæces, which formed so striking a feature in the economy of Plumatella, was frequently observed to take place from the anal orifice.

The vascular system consisted, as far as could be seen, of an artery which passed up the axis of the body, in close connection with the gullet, until it arrived at the tentacular cup on its concave side; it there divided at right angles into two branches, which passed within and around the tentacular cup, and sent a capillary twig into each of the tentacles. These capillaries had distinctly contractile walls, and were loosely attached by cellular tissue to one side only of the cavity of the tentacle. (See woodcut.)

The artery pulsated rather irregularly at the rate of about fifteen beats in the minute, and at each pulsation a wave of red blood (red blood globules floating in a pale liquor sanguinis) passed, like a railway train, along the artery and its branches up into the very end of the hollow tentacles. The blood, after momentarily resting in the capillaries of the tentacles, was ejected from them by an undulating contraction of the walls of those vessels, c and returned in a regularly-flowing stream along the venous system. The venous system was first detected as four branches, viz., one from the

outside, and another from the inside,

a, wall of tentacle; b, capillary containing blooding tentacles. globules; c, membrane unit

b

of each of the horns of the crescentic tentacular cup. The two branches on each side immediately united, and the two

vessels thus formed encircled the gullet, and united to constitute a single vein, which traversed the axis of the body on the side of the gullet opposite to that occupied by the artery.

I have stated that the blood, urged by the contractile artery, passed at once into the interior of the tentacles, and sometimes such appeared to be the case; but it frequently happened that the globules were observed ascending some of the tentacles at the same time that they were descending others in their immediate vicinity. Hence I think we must suppose some auxiliary propelling apparatus to be interposed between the artery and the tentacular capillaries. The opacity of the cup, from which the tentacles spring, not only prevented me from detecting any such arrangement, but also from observing the mode of communication between the capillaries and the venous system. The muscular system consisted of a layer of flat longitudinal bands immediately beneath the integument, and interior to these fine circular fibres could be traced with extreme difficulty under a power of 300 diameters. The viscera were retained in their place by delicate areolar fibres.

The second animal I have to describe, and which is probably another species of the last, was found in a decayed oyster shell dredged from the Firth of Forth near Inchkeith. The shell was inhabited by Clione celata, and while examining the projecting processes of the sponge, I noticed a great number of animals which I for some time mistook for Lepralia, until my attention was arrested by a slight want of symmetry in the circle of the tentacles. It was not a circle, but rather an oval very slightly flattened on one side. A power of 200 diameters was brought to bear on one of the animals, and it appeared as shown in fig. 2, Plate VII. The body, slightly projecting from a membranous tube buried in the shell, carried a crown of eighteen tentacles finely ciliated, but not presenting the appearance of moving teeth. They were not connected. by membrane at their base. Within the tentacles, a constant stream of blood globules ascended and descended precisely as in the animal before described in this communication, but the opacity of the cup prevented the detection of any larger vessels. I succeeded in digging one only of these animals with its tube entire from the shell. It was about half an inch in

316 Existence of Thread-Cells on the Tentacles of Cydippe. length. The long gullet terminated in a globular gizzard, the interior of which was paved with bodies apparently cartilaginous, and of prismatic shape. The gizzard communicated below with a thick walled stomach. No ascending rectum was detected; but I inferred it to exist, hidden behind the stomach, as a thin membranous tube containing fusiform fæces was observed passing upwards to the tentacular crown. The blood vessels were displaced, and lying twisted together within the body.

These animals have been examined by the most eminent naturalists in this city, who consider that they possess great interest. They appear to me to possess characters common to the Polyzoa (Plumatella, Pedicellina), the Tunicata (in which the circulation of red blood has been noticed by Milne-Edwards), and the Annelida, in which last class they probably ought to take their place. I propose to designate the first of these animals Phoronis hippocrepia, the second Phoronis ovalis.

On the existence of Thread-Cells on the Tentacles of Cydippe. By T. STRETHILL WRIGHT, M.D., &c.

In my description of the tentacles of Cydippe, contained in the last number of this Journal, I stated that their surfaces were crowded with minute thread-cells. I was therefore surprised to find it remarked by Professor Huxley (Medical Times and Gazette, June 21, 1856), that true thread-cells had not been observed in the Beroida, to which class Cydippe belongs. At that time the Firth of Forth was swarming with a small variety of Cydippe, distinguished by the rufous colour which tinged the bases of the tentacular cirri. The amputated tentacles of this species adhered with extreme tenacity to bodies applied to them. When examined under a power of 300 diameters, they were seen to be so closely studded with

small cells, that their surface had a granular appearance. These cells were spherical, and opaque from the presence of molecular matter in their interior. When ruptured by pres

*PHORONIS, one of the surnames of Isis.