direction, and situated at the entry of the mouth, between the internal labial processes. These laminæ are twenty in number, and are from one to two lines in breadth, and from four to five in length, but diminish in this respect towards the sides. They are supplied by nerves from the small ganglions which are connected to the ventral extremities of the anterior sub-œsophageal ganglions."† IV. SIGHT. That the tunicated and bivalved mollusca are destitute of eyes has been long an axiom with conchologists, but recently some exceptions, of a somewhat doubtful character it must be confessed, have been pointed out. Placed between the oral tentacula, as also between the filaments of the vent, of certain Ascidia, there is a series of eight and six little scarlet globular points, which are so like the organs that Ehrenberg affirms to be eyes in the medusæ and starfish, that it is impossible to doubt the sameness of their functions. So also in a few bivalves, of which the Pectens and Sphondyli are the most eminent examples, there are many green metallic lustrous beads placed, at stated intervals, on the margins of the cloak among the tentacular filaments (Fig. 33). The use of these beautiful organs re Fig. 33. mained unguessed, until Poli gave it as his opinion that they were subservient to vision; whence he named the animal of the Pecten, after Juno's watchman, the Argus, to whose mantle you may suppose the hundred eyes of the fabled son of Aristor had been transferred. How far Poli's "No organs having the most distant relation to the sense of vision, have ever been observed in any of the acephalous or bivalve mollusca."-ROGET'S Bridgew. Treat. ii. 481. opinion may be correct, I cannot say; but a physiologist of great ingenuity has inferred that in the bivalves in question there is a sense analogous, at least, to that of ordinary vision, from their quick and varied motions, and from the fact that the Trigoniæ, in their attempts to escape from a boat, leap in a definite direction, as Mr. Stuchbury had witnessed. † The great majority of the Pteropods, though apparently influenced by light, and a few marine naked Gasteropods, are eyeless; § but organs which have been generally considered as serving the purposes of vision, have been bestowed on all other mollusca. There can be no question of their function in the Cephalopods, for in them the eyes are very large, and similar, in all essential points, to those of vertebrate animals. They are two in number, one on each side of the "Each of these ocelli possesses a cornea, lens, choroid, and nerve: they are, without doubt, organs of vision."-GARNER in Mag. Nat. Hist. n. s. iii. 128.-" Will has instituted researches on the eyes of the Conchifera He found them to be very highly organised. Besides Pecten, Sphondylus, and Ostrea, he found them also in Pinna, Arca, Pectunculus, Mytilus, Cardium, Tellina, Mactra, Venus, Solen, Pholas, sometimes in vast numbers."-Reports on Zoology for 1844, p. 439, printed for the Ray Society, Lond. 1847. + Carpenter's Gen. and Comp. Phys. pp. 98, 99. The figure is a view of the eye of Octopus vulgaris, copied from Cuvier. a a, A cellular and muscular tunic, the latter for opening the lids; bb, the conjunctiva; c, another tunic, enveloping the globe of the eye, and a pouch situated behind it (e), containing (f) the optic ganglia, and the glands which surround it (g). The pouch (e) is a transparent membrane, which occupies all the space between the globe of the eye and the tunics which go to its lids; so that the former actually fills only about a third of the greater globe, which, at first view, appears to be the eye itself. hh, The external coat of the proper eye, perforated with an infinite number of minute holes, for the passage of the filaments from the optic ganglion; and i, another coat, formed apparently by the expansion and netting of these nervous filaments. m, The crystalline lens. I may also refer to a description and figure of Loligo sagittata in the Edinb. Journ. Nat. and Geogr. Sc. iii. 286. The existence of eyes in Doris and Goniodoris,-genera that had hitherto been described as entirely devoid of these organs,-has been proved by my friends Alder and Hancock, of Newcastle. They are to be most distinctly observed in young individuals.-Ann. Nat. Hist. ix. 31. head; they are capable of being moved to a slight extent; they are formed with coats, humours, and nerves, so arranged that, on physical grounds alone, we may confidently pronounce them to be optical instruments of considerable power (Fig. 34). The structure is most perfect in the Loligo and Sepiæ; it is less so in the Octopus; and in the Nautilus has become so simplified that there is some reason to suppose the sense of sight in it to be reduced to the simple consciousness of the reception of light. The case is greatly different with the reputed eyes of the Gasteropod mollusca. From their minuteness it is difficult to unravel their structure; and, in many instances, they are so situated that, were they organs of vision, the creature, it is presumed, could be little benefited by them. Moreover, it has been asked of what avail it would be for an animal to discover distant objects, which could neither overtake them if necessary for food, nor avoid them if inimical to its existence; and it has been asserted that the eyes of snails, at least, are in every respect insensible to light, for the creatures creep and climb as correctly in the dark as by daylight; they do not at any time perceive obstacles, placed on purpose in their way, until they touch them; and when deprived of the organs they crawl on as unconcernedly, and guide themselves as safely, as they did previously to the mutilation. On these grounds some naturalists of eminence have denied that the little black points, denominated eyes by the vulgar and the learned, are ocular bodies, and find in them nothing more than the organs of an exquisite sense of touch. * Organs of touch they may be in Snails (Helix, Limax, &c.), in which they are elevated on movable and filiform tubes capable of being directed to all points; but organs of touch they surely cannot be in the greater number of the class, on which they are placed, as it were purposely, to be removed from the contact of external objects. Such, for example, is their position in the Whelks (Buccinum) and Rockshells (Murex), in the Lymnæidæ, Turbonidæ, and others. Seeing, too, how amply the mollusca are otherwise furnished with tactic organs, additional ones might be deemed superfluous; and, notwithstanding the facts opposed to it, I am firmly of opinion that what have been called the eyes have been properly so designated,-organs susceptible not merely of the impressions of light, but capable of distinguishing ob *Gaspard in Zool. Journ. i. 179. Also, Lister in Phil. Trans. abridg. ii. * jects, and perhaps colours. They are placed on the anterior part of the body, as the eyes of every other animal are; their size and number are constant in individuals of the same species; they bear a very exact resemblance to the eyes of many insects, and to the stemmata of others, which are believed to be eyes; and the snail, when confined, makes unequivocal attempts to turn that part of the body which is furnished with them to the light." I have occasionally, on a summer's dewy evening, when the animals were on the alert, made experiments on our common slugs and snails; and I am satisfied, as Lister appears to have been, † that they do perceive obstacles placed in their way, diverging from them when within from one to three inches. They rarely touch the opposing substance, but often they alter their course so slightly as to pass it by in freedom with a shortening of the tentaculum on the near side, while sometimes the track is changed entirely. Nay, I have seen, or imagined I have seen, in more than one instance, a snail follow, with apparent eagerness, the purple-coloured flower of a thistle held near its tentacula, and gradually withdrawn. Adanson very readily distinguished the lens and iris in the eyes of the Cyprææ, whose sight, he asserts, is pretty acute-"assez fin; "§ and Swammerdam affirms that the Littorina littorea draws itself suddenly within the shell when anything is suddenly presented to its eyes; "so that," he adds, "I may venture to affirm from hence, that this is the only species of snails that I know wherein any manifest signs of sight appear." || Further, such mollusca as have oculiferous tentacula do not use them in touching objects; for, as Mr. Guilding has properly observed, they carry them usually erect; and the inferior ones, with the lobes of the cheeks, are principally used as tactors. I grant to you that these arguments are not decisive of the question, and that one drawn from the anatomical structure of the organs would be of superior convincement; and that argument is now, thanks to the dexterity of modern anatomists, entirely in my favour. In the Cypræadæ and the allied families, the structure of the eye is said to be by no Müller, Verm. Hist. i. præf. 3. et 4. + Lister's Exercit. Anat. de Cochleis, p. 10. 1694, 12mo. "Experiments are said to have been recently made, both by Leuchs and by Steifensand, in which a snail was repeatedly observed to avoid a small object presented near the tentaculum; thus affording evidence of its possessing this sense."-ROGET's Bridgw. Treat. ii. 482. § Senegal, p. 71. Book of Nature, p. 81. * means obscure; and the giant Strombidæ, which inhabit the Caribbean Sea, have eyes more perfect than those of many vertebrated animals. They have, according to the late Rev. Lansdown Guilding, a most intelligent and indefatigable naturalist, a distinct pupil and a double iris, equalling in beauty and correctness of outline those of birds and reptiles; and he discovers in the organ a vitreous and an aqueous humour, and the black pigment. † Mr. Gray, a naturalist of equal industry and accuracy, tells us that if they who have doubted concerning the nature of these organs "had examined the eyes of the marine carnivorous mollusca, Buccinum undatum or Fusus despectus, and more especially some of the larger Strombi, they would have found the eye as fully developed as in the cuttle-fish, showing the cornea and the nearly orbicular crystalline lens almost perfectly formed, as may be seen by any person simply cutting the cornea across, and slightly pressing it, when the crystalline lens will protrude." This evidence seems conclusive; for if the same parts cannot be demonstrated in the smaller or in the terrestrial mollusca, it is surely because of the minuteness of the organ and the difficulty of the dissection. But the fact is, that Swammerdam has described, with great minuteness, the eye of the common snail, in which he detected "five distinct and visible parts," viz. the uvea, the aqueous, the crystalline, and the vitreous humours, with the arachnoid tunic; parts which, he affirms, were as "clear as the sun at noon. He likewise observed that the eyes of the Lymnæi were provided each with "its own proper crystalline humour." The accuracy of this description has been denied, as indeed this good man, and incomparable anatomist, seems to have foreseen would be the case. "But who can credit this?" says he; "for it seems indeed improbable, that on a point not bigger than the nib of a writingpen, such exquisite art, and so many miracles, should be displayed." § See Blainville's anatomy of the eye of Voluta cymbium, L., in his Princ. d'Anat. Comp. i. 445. + Zool. Journ., iv. 172. Also, Swainson on Hab. and Inst. of Anim. p. 43. "In the typical Strombi, these organs are so much developed that the iris is richly coloured, and the eyes of some of the larger species have been described to us as particularly beautiful."-SWAINSON'S Malacology, 136. Edinb. Journ. Nat. Geogr. Sc. iii. 52. Of Swammerdam's anatomy of the Snail, Cuvier says, "Il en fait connaître toutes les parties, le cœur, les viscères, le foie; il en décrit tous les muscles, et explique toutes les manières dont cet animal est attaché à sa coquille. Il fait connaître ses yeux, leur cristallin, la nerf optique qui s'y rend |