cal importance among the earliest inhabitants of the ancient deep.* The extensive range which it formerly occupied among the earliest inhabitants of our Planet, may be estimated from the fact, that the Crinoïdeans already discovered have been arranged in four divisions, comprising nine genera, most of them containing several species, and each individual exhibiting, in every one of its many thousand component little bones,† a mechanism which shows them all to have formed parts of a well-contrived and delicate mechanical instrument; every part acting in due connexion with the rest, and all adjusted to each other with a view to the perfect performance of some peculiar function in the economy of each individual. The joints, or little bones, of which the skeletons of all these animals were composed, resemble those of the starfish their use, like that of the bony skeleton in vertebral animals, was to constitute the solid support of the whole body, to protect the viscera, and to form the foundation of a system of contractile fibres pervading the gelatinous integument with which all parts of the animal were invested.‡ The bony portions formed the great bulk of the animal, as they do in star-fishes. The calcareous matter of these little bones was probably secreted by a Periosteum, which * The monograph of Mr. Miller, exhibiting the minute details of every variation in the structure of each component part in the several Genera of the family of Crinoïdea, affords an admirable exemplification of the regularity, with which the same fundamental type is rigidly maintained through all the varied modifications that constitute its numerous extinct genera and species. These so-called Ossicula are not true bones, but partake of the nature of the shelly Plates of Echini, and the calcareous joints of Starfishes, As the contractile fibres of radiated animals are not set together in the same complex manner as the true muscles of the higher orders of animals, the term Muscle, in its strict acceptation, cannot with accuracy be applied to Crinoïdeans; but, as most writers have designated by this term the more simple contractile fibres which move their little bones, it will be convenient to retain it in our descriptions of these animals, in cases of accident, to which bodies so delicately constructed must have been much exposed in an element so stormy as the sea, seems to have had the power of depositing fresh matter to repair casual injuries. Mr. Miller's work abounds with examples of reparations of this kind in various fossil species of Crinoïdeans. Our Pl. 47, Fig. 2, a. represents a reparation near the upper portion of the stem of Apiocrinites Rotundus. In the recent Pentacrinus (Pl. 52, Fig. 1,) one of the arms is under the process of being reproduced, as Crabs and Lobsters reproduce their lost claws and legs, and many lizards their tails and feet. The arms of star-fishes also, when broken off, are in the same manner reproduced. From these examples we see that the power of repro duction has been always strongest in the lowest orders of animals, and that the application of remedial forces has ever been duly proportioned to the liability to injury, resulting from the habits and condition of the creatures in which these forces are most powerfully developed. Encrinites Moniliformis, As the best mode of explaining the general economy of the Crinoïdea, will be to examine in some detail the anatomy of a single species, I shall select, for this purpose, that which has formed the type of the order, viz. the Encrinites moniliformis (see Pl. 48, 49, 50.) Minute and full descriptions are given by Parkinson and Miller of this fossil, showing it to combine in its various organs a union of mechanical contrivances, which adapt each part to its peculiar functions in a manner infinitely surpassing the most perfect contrivances of human mechanism. Mr. Parkinson* states that after a careful examination he has ascertained that, independently of the number of pieces. * Organic Remains, vol. ii, p. 180, which may be contained in the vertebral column, and which, from its probable length, may be very numerous, the fossil skeleton of the superior part of the Lily Encrinite (Encrinites Moniliformis) consists of at least 26,000 pieces. See Pl. 50, Figs. 1, 2, 3, 4, &c.* Mr. Miller observes that this number would increase most surprisingly, were we to take into account the minute calcareous plates that are interwoven in the integument covering the abdominal cavity and inner surface of the fingers and tentacula.† We will first examine the contrivances in the joints, of the vertebral column, which adapted it for flexure in every direction, and then proceed to consider the arrangement of other parts of the body. These joints are piled on each other like the masonry of a slender Gothic shaft, but, as a certain degree of flexibility was requisite at every articulation, and the amount of this flexure varied in different parts of the column, being least at the base and greatest at the summit, we find proportion * Bones of the Pelvis. Ribs Clavicles Arms. Six bones in each of the ten arms Hands. Each hand being formed of two fingers, and cach make 5 5 5. 60 800 1800 .24,000 Total 26,680 30 proceeding, on the average, from each of the † Although the names here used are borrowed from the skeleton of verte. brated animals, and are not strictly applicable to radiated Echinoderms, it will be convenient to retain them until the comparative anatomy of this order of animals has been arranged in some other more appropriate manner.. ate variations both in the external and internal form and dimensions of each part.* The varieties of form and contrivance which occur in the column of a single species of Encrinite, may serve as an example of analogous arrangements in the columns of other species of the family of Crinoïdeans, (see Pl. 47. Figs. 1, 2, 5, and Pl. 49. Fig. 4 to Fig. 17.†) The body (Pl. 49, Fig. 1) is supported by a long vertebral column attached to the ground by an enlargement of its base (Pl. 49, Fig. 2.) It is composed of many cylindrical thick joints, articulating firmly with each other, and having a central aperture, like the spinal canal in the vertebra of a quadruped, through which a small alimentary cavity descends from the stomach to the base of the column, Pl. 49, Fig. 4, 6, 8, 10. The form of the column nearest the base is the strongest possible, viz. cylindrical. This column is interrupted, at intervals, which become more frequent as it advances upwards, by joints of wider diameter and of a globular depressed form (Pl. 49, Fig. 1, and Figs. 3, 4, a, a, a, a.) Near the summit of the column, (Pl. 49, Figs. 3, 4,) a series of thin joints, c, c, c, is placed next above and below each largest joint, and between these two thin joints, there is introduced a third series, b, b, b, of an intermediate size. The use of these variations in the size of the interpolated joints was to give increased flexibility to that part of the column, which being nearest to its summit required the greatest power of flexion. At Plate 49, Figs. 6, 8, 10, are vertical sections of the columnar joints 5, 7, 9, taken near the base; and show the internal cavity of the column, to be arranged in a series of double hollow cones, like the intervertebral cavities in the back of a fish, and to be, like them, subsidiary to the flexion of the column; they probably also formed a reservoir for containing the nutri. tious fluids of the animals. The various kinds of Screw stone so frequent in the chert of Derbyshire, and generally in the Transition Limestone, are casts of the internal cavities of the columns of other species of Encrinites, in which the cones are usually more compressed than in the column of the E. moniliformis. At Pl. 49, Fig. 4 is a vertical section of Fig. 3, being a portion taken from near the summit of the column, where the greatest strength and flexure were required, and where also the risk and injury and dislocation was the greatest; the arrangement of these vertebræ is therefore more complex than it is towards the base, and is disposed in the following manner (see Fig. 4.) The vertebræ, a. b. c. are alternately wider and narrower; the edges of the latter, c. are received into, and included within, the perpendicularly length The name of Entrochi, or wheel stones, has with much propriety been applied to these insulated vertebræ. The perforations in the centre of these joints affording a facility for stringing them as beads, has caused them, in ancient times, to be used as rosaries. In the northern parts of England they still retain the appellation of St. Cuthbert's beads. On a rock by Lindisfarn Saint Cuthbert sits, and toils to frame The sea-born beads, that bear his name. MARMION. Each of these presents a similar series of articulations, varying as we ascend upwards through the body of the animal, every joint being exactly adjusted, to give the requisite amount of flexibility and strength. From one extremity of the vertebral column to the other, and throughout the hands ened margin of the wider, a. b.; the outer crenulated edge of the narrower included vertebræ, articulate with the inner crenulated edge of the wider vertebræ, which thus surround them with a collar, that admits of more oblique flexion than the plane crenulated surfaces near the base of the column, Figs. 9, 10, and at the same time renders dislocation almost impossible. To these is superadded a third contrivance, which still farther increases the flexibility and strength of this portion of the column, viz. that of making the alternate larger joints, b. b. considerably thinner than the larger collar joints, a. a. The figures numbered from 11 to 26 inclusive, represent single vertebræ taken from various portions of the column of Encrinites moniliformis. The joints at Figs. 11, 13, 15, 17, 19, 21, 23, 25, are of their natural size and in their natural horizontal position, and show, at the margin of each, a crenated edge, every tooth of which articulated with a corresponding depression near the margin of the adjacent joint. The stellated figures (12, 14, 16, 18, 20, 22, 24, 26,) placed beneath the horizontal joints to which they respectively belong, are magnified representations of the various internal patterns presented by their articulating surfaces, variously covered with an alternate series of ridges and grooves, that like the cogs of two wheels, articulate with corresponding depressions and elevations on the surfaces of the adjacent vertebræ. |