The only other calcareous coverings that re main to be noticed are the rudimentary valves in Otion and Cineras, animals that bear a general resemblance in form to Anatffa, but which are covered chiefly by a semicartila ginous tunic. There are two small valves in. Otion, which are attached to the anterior as pect just above the brachial orifice. In Cine ras they are five in number, two in the same situation as those of Otion, two along the ter minal margin of .the outer tunic, and one unpaired along the dorsal aspect. These are imbedded by their margins in the semi-carti laginous tunic, and seem to be formed by it ; calcareous matter being added to their margins in successive layers.
The ligamentous membrane, by which the valves in Anatifa are connected one with the other and with the peduncle, is strong but pliant. It is an extension of the outer cover ing of the peduncle. At the brachial orifice, it is reflected inwards to join the mantle. In addition to this, each valve has a membrane of its own, which closely invests its inner sur face, and is not continuous with those of the other valves. The peduncle of this and the allied genera may be considered as a kind of developed ligament. . If we regard the upper pair of valves as analogous to the valves of Aceplialous Mollusca, the peduncle is found to be attached to them at points corresponding to the situation of the ligament in those shells. This organ is sometimes of great size. In the British seas it occasionally occurs two feet in length. Its epidermis is generally rough, wrinkled transversely, coriaceous, and elastic : Otion, however, has it very smooth and stiff, nearly cartilaginous, diaphanous. In some species it is so elasCc as to admit of exten sive lateral motion, and much elongation and contraction. These movements are effected by a layer of strong muscular tissue beneath the skin, within which there is a large organ, granular in its structure, regarded by some anatomists as the ovary. Burmeister is of opinion that the peduncle is merely an organ of support : and he suggests that the granular parenchymatous mass, which fills its interior, is destined solely for its own nutrition, which he seems to think is independent of the other parts of the animal. In most species, it is by its epider mis that the peduncle adheres. The peduncle pre sents still other varieties than those just mention ed. Pollicipes villosus has itcovered partly with imbricated scales, and partly with a hairy coat ; and Pollicipes guadrivalvis has its valves wholly encased in a large prolongation of the pe duncle, which, on its upper surface, bears four valves arranged nearly in the same way as those of the opercule of the Balanids. The base of Coronula is closed by a strong fibrous membrane connected with the body of the animal only by a process of the epidermis. It is regarded by Burmeister as, the analogue of the peduncle of the Lepads.
The cartilaginous tunic of Otion Cuvieri, at its summit, is enlarged into. two large auri form appendages, hollow, having a crescentic orifice externally, and internally commu nicating with the visceral cavity -of the animal ; no organ is discoverable within them, but their cavities receive the terminations of a duct, which descends. on the dorsal. aspect of the body in the groove of the dorsal valve, from the peduncle.
Of the mantle, as. one of the tegumentary organs of the Cirripeds, little more need be said, than that it is generally a very thin trans parent membranous sac, surrounding the vis ceral mass, open only at the brachial orifice, where it joins the epidermis and.intervalvular
ligament, and is reflected. so as to form an inner lining for the visceral cavity-. It has neither fringes of filaments, n-or foliated pro cesses. M. St. Ange describes another tunic. of the visceral mass, which, he savs,. is con7 tinuous with the horny covering of tiie arms.
Locoinotion.—Their base being permanently fixed, the principal motions of the Cirripeds are those of the arms, which seem to be sub servient at once to the respiratory and. to tho digestive functions. But, as has just .been, mentioned above, the peduncle of Anatifa and. other allied crenera is moved both.laterally and; in the way obf contraction and extension, and! the valves, in the same animals, are. so moved as to open and close:the brachial. orifice. The. motions of the arms are, in many species, very rapid, and are performed with great re gularity; proving the existence of a complete muscular apparatus. both at their bases and; within their numerous joints ; but the parts are. too minute to admit of a satisfactory examina tion being inade of their structure. The Lepads, have a strong transverse adductor muscle placed between their superior valves, just above the brachial orifice (a,fig.340); this muscle seems. to be every way analogous to the same 'organ in Acephala. Its action closes the brachial slit very accurately ; while its^ relaxation admits of its being opened by the advance of the arms grouped together into the form of a wedge. This movement of the arms cannot be per formed without the whole body being carried outwards; which is effected apparently by the contraction of certain delicate muscular fibres spread over the mantle, and attached around' the margin of the orfiee. Cuvier describes a similar set of fibres, " attached to the mantle opposite the insertion ef the peduncle, by the action of which the general mass of the body is drawn deeply within the shell." This we have failed to observe in the species which have come under our notice. When the arms are fully exserted, they are separated one from the other, fan-like. This motion is probably produced by a muscular expansion, described by M. St. Ange as covering the visceral mass dorsally, the fibres of which are grouped into six bundles on either side, cor responding to the arms. The same observer describes also certain tendons which he found crossing one another at the median line ; these are probably connected with another layer of rnuscles, expanded over the dorsal surface of the visceral mass, fitted to approximate the arms of either side towards one another. The muscles of the jaws cannot be satisfactorily examined on account of their minuteness. In the Balanids, the valvular opercule is moved by a set of muscles attached to the circle of shelly plates that surround the openingr of the parietal cone. Its adductors, which close the aperture with great force, are attached to the extremities of the valves on either side. The visceral mass is, in the Balanids, fixed to the shell by three muscular bands, partly attached, around the mouth, to a process of the epider mis, and partly spread over the mantle.