Structure of the tentacular suckers in the Cephalopoda.

Fig. 281. Structure of the tentacular suckers in the Cephalopoda.

Onychoteuthis, showing the structure of the arms.

Fig. 282. Onychoteuthis, showing the structure of the arms.

Nor is this all that claims our admiration in the organization of the arms of Onychoteuthis: at the base of each fleshy expansion that supports the tenacious and fanged suckers above described is a small group of single adhesive disks, by the assistance of which the two arms can be locked together (fig. 282, a), and thus he made to cooperate in dragging to the mouth such powerful or refractory prey as, singly, the arms might be unable to subdue - an arrangement which has been rudely imitated in the construction of the obstetric forceps*.

(1512). The Argonaut constitutes the type of another family of the Cephalopoda, and is remarkable as being the inhabitant of a shell of exquisite beauty, familiarly known as that of the Paper-Nautilus - a shell which, from remote antiquity, has been decorated with all the ornaments of fiction, and celebrated alike by Poetry and her sister Arts. (1513.) It was, indeed, to this Cephalopod that the ancients assigned the honour of having first suggested to mankind the possibility of traversing the sea in ships; and nothing could be more elegant than the little barque in which the Argonaut was supposed to skim over the waves, hoisting a pair of sails to the breeze, and steering its course by the assistance of oars provided for the purpose.

Argonaut (Argonatda Arqo.) (After Poli.)

Fig. 283. Argonaut (Argonatda Arqo.) (After Poli).

* Cyclopaedia of Anatomy and Physiology, art. Cephalopoda.

(1514). The figure annexed (fig. 283), given by Poli in his magnificent work already referred to*, was in perfect accordance with the generally-received opinion; and on such respectable authority we are not surprised to find Cuvier assenting to and sanctioning the statement that, when the sea is calm, fleets of these little sailors might be seen navigating its surfaee, employing six of their tentacula or arms instead of oars, and at the same time spreading out two, which are broadly expanded for the purpose, instead of sails. Should the waves become agitated, or danger threaten, the Argonaut, as we are told, draws in his arms, lowers his sail, and, settling to the bottom of his shell, disappears beneath the waters.

(1515). It is a thankless office to dispel the pleasant dreams of imagination; yet such becomes our disagreeable duty upon this occasion. M. Sander Rang, in a recently-published memoir upon this subject 1, has, from actual observation, apparently established the following facts: - 1st, that the belief, more or less generally entertained since the time of Aristotle, respecting the skilful manoeuvres of the Poulpe of the Argonaut in progressing by the help of sails and oars on the surface of the water, is erroneous. 2nd. The arms which are expanded into membranes have no other function than that of enveloping the shell in which the animal lives, and that for a determinate object to be explained hereafter. 3rd. The Poulpe, with its shell, progresses in the open sea in the same manner as other Cephalopods. And lastly, that when at the bottom of the ocean, the Argonaut, covered with its shell, creeps upon an infundibuliform disk, formed by the junction of the arms at their base, and presenting (alas!) the appearance of a Gastero-pod mollusk.

(1516). It is not a little remarkable that the same animal should, even in these days, be the subject of the extremes of credulity and scepticism; yet such has been the case with the Argonaut. While zoologists were contented to allow the creature in question the reputation of being an active and skilful navigator, it has been very generally stigmatized as a pirate, which, having forcibly possessed itself of the shell of another animal, lived therein, and made use of it for its own purposes. It was in vain to urge, in opposition to this calumny, that the Argonaut was never found in any other shell than the beautiful one represented in the preceding figure; that no other creature had been pointed out as the real fabricator of its abode; that, whatever the size of the Poulpe, it occupied a residence precisely corresponding in dimensions with those of the possessor. The apparent want of resemblance between the outward form of the animal (fig. 285) and that of its fragile covering, together with the absence of any muscular connexion between the two, were looked upon as furnishing sufficient evidence of its parasitical habits. The careful observations of Madame Jeannette Power, to be noticed more at length hereafter, and those of M. Sander Rang, above alluded to, have, however, completely settled the so long agitated question; and, the Argonaut having been watched carefully from the state in which it leaves the egg until it arrives at maturity, the manner in which it forms and repairs its frail shell is now satisfactorily understood.

* Testacea utriusque Sicilian.

1 Guerin's' Magasin de Zoologie.' Translated in the Magazine of Natural History, vol. iii. new series, p. 521.

(1517). A still more interesting group of Cephalopods, and one which in former periods of the world has been extensively disseminated, inhabited chambered shells. But of all the varied forms of these creatures, whose remains are so abundantly met with in a fossil state, and known by the names of Ammonites, Belemnites, Nummulites, etc, two species only have been found to be at present in existence: - the Spirula, an animal as yet imperfectly known, and the Nautilus Pompilius, of which the only specimen obtained in modern times* has been the markable feature, however, exhibited in the external conformation of Nautilus is the conversion of the sucker-bearing arms of other Cepha-lopods into an elaborate apparatus of tentacular organs appended to the head (o o); but these, as well as the eye (m), will be more minutely described as we proceed.