are concealed within the bodies of their snails are always white, as are also those which live in holes whence they never issue. Another striking proof of the blanching effect of darkness is furnished by some bivalve shells permanently affixed by their lower valve, which is constantly white, while the upper one may possibly be variegated with bright colours. The Spondyli, and a number of Pectens, afford examples of this contrast between their valves. Olivi has further remarked, that the shells which are enveloped in sponges, or other foreign bodies, or which burrow in sand, or even which live in constantly shaded places, are much paler than those which crawl about unprotected from the light; and even the exposed parts of the same shell are more highly coloured than the parts which are shaded.

On this point, Professor Edward Forbes has the following remarks:-"A comparison of the Testacea and other animals of the lowest zones with those of the higher, exhibits a very great distinction in the hues of the species, those of the depths being for the most part white or colourless, whilst those of the higher regions, in a great number of instances, exhibit brilliant combinations of colour. The results of an inquiry into this subject are as follows:

"The majority of shells of the lowest zone, are white or transparent if tinted, rose is the hue: a very few exhibit markings of any other colour. In the seventh region, white species are also very abundant, though by no means forming a proportion so great as in the eighth. Brownish-red, the prevalent hue of the Brachiopoda, also gives a character of colour to the fauna of this zone: the Crustacea found in it are red. In the sixth zone, the colours become brighter, reds and yellows prevailing, generally, however, uniformly colouring the shell. In the fifth region many species are banded or clouded with various combinations of colours, and the number of white species has greatly diminished. In the fourth, purple hues are frequent, and contrasts of colour common. In the third and second, green and blue tints are met with, sometimes very vivid, but the gayest combinations of colour are seen in the littoral zone, as well as the most brilliant whites.

"The animals of Testacea, and the Radiata of the higher zones, are much more brilliantly coloured than those of the lower, where they are usually white, whatever the hue of the shell may be. Thus, the genus Trochus is an example of a group of forms mostly presenting the most brilliant hues, both of shell and animal; but whilst the animals of such species as inhabit the littoral zone, are gaily chequered

with many vivid hues, those of the greater depth, though their shells are almost as brightly coloured as the coverings of their allies nearer the surface, have their animals for the most part of an uniform yellow or reddish hue, or else entirely white.

"The chief cause of this increase of intensity of colour as we ascend, is doubtless the increased amount of light above a certain depth. But the feeding grounds of the animals would appear to exert a modifying influence, and the reds and greens may be in many cases attributed to the abundance of nullipore, and of the Caulerpa prolifera, a sea-weed of the most brilliant pea-green, the fronds of which the Mollusca of that colour, such as Nerita viridis, make their chosen residence."*

And now I bid you a short farewell with the repetition of my former advice, to learn the nomenclature of this little corner of natural history, by an actual examination of examples in your own collection; and you might conduct that examination in such a sure way, that it will lead you to discover the position of the object in the system, and the name it bears amongst those with whom you wish in future to hold occasional converse. Listen to the words of one of the greatest of men in modern times:

"Natural history, in fact, is one of those sciences in which genius is impotent, unless seconded by power; and the efforts of power vain, unless its results are arranged by the co-operation of genius.-The names, which man is ordered to impose, are not incoherent signs applied by chance to some isolated objects. To render them appropriate and significant, the objects, as it is said, must pass before the namer; in other words, he must compare these objects, apprehend the relations of their similarity and difference, and classify them; which he cannot do unless he see them together, and make himself intimately acquainted with them. In short, to name well, taking the word in its fullest acceptation, it is necessary not only to know well, but, it may be said, to know all. The superstition of the Cabalists believed in the magic power of names. This was a false consequence of a principle, that names, were they perfect, would represent the essence and aggregate of things.

"Such is the object of this department of science, which unreflecting minds would doom to contempt, under the name of Nomenclature. To refute their assertions, it is only necessary to repeat the fundamental condition which we

* On Algean Invertebrata, in Reports Brit. Assoc. 1843, p. 172-3.

have just announced, namely, that to name well, it is necessary to know well.'

If this passage may appositely close this letter, it may with equal propriety furnish a motto for my next; and incline you to lend a more willing ear to my exposition of system after system, each of them being the best index you can have to the condition of Conchology at the period of its publication.

* Cuvier in Edinb. New Phil. Journ. April 1829, p. 2.

492

LETTER XXVI.

THE HISTORY OF CONCHOLOGY FROM ARISTOTLE TO

CUVIER.

THE foundations of Conchology were laid by Aristotle on those broad and rational views which characterize all his works on the Natural History of Animals, and which are worthy of his own reputation as a philosopher, and of the inquisitive and intelligent society to whom they were delivered. The structure and habits of the creatures embraced in this section of natural science were the main objects of his study, while their relations to the other animated entities by which they are surrounded, and their own mutual affinities were not forgotten, although undoubtedly the classification of them appears to have been considered a matter of secondary importance, and such as it is, was rather forced upon him than invented to give some degree of method and generalization to the expression of the results of his inquiries. To censure this Father for the incompleteness, or even his want of a conchological system, is inconsiderately done, for it must be obvious that no system can be otherwise than defective and artificial until discovery has, in a long and lingering progress, collected together a large magazine of materials, among which there shall at least be found a type of every modification of structure exhibited in the class.* But in his age the number of shells known was very confined, and to have advanced beyond the primary divisions of them into univalves, bivalves, and turbinated kinds, could be of no possible utility, and might have been hurtful to a further progress, for "the over early and peremptory reduction of knowledge into arts and methods" is an error from which, as Bacon has justly remarked, "sciences receive small or no augmentation."†

"Cependant comme Aristote n'a pas jugé nécessaire de former un cadre zoologique, quelques personnes ont prétendu que son ouvrage manquait de méthode. Assurément ces personnes n'avaient qu'un esprit très superficiel."-CUVIER, Hist. des Sc. Ñut. i. 147.

"Another error, of a diverse nature from all the former, is the overearly and peremptory reduction of knowledge into arts and methods; from which time commonly sciences receive small or no augmentation. But as young men, when they knit and shape perfectly, do seldom grow to a further

His views were higher, and his researches were pushed in the only direction in which they could be made available. He has left us a history of the Cephalopods remarkable for its fulness and accuracy, and equally remarkable for its exemption from the marvels and puerilities which disfigure the same history as delivered by his successors; and although there may be less of observation and fact in his account of the shelled Molluscans, yet we find the same ends kept ever in view, and the incessant effort to attain his object by attention to the habits of the animals, and an examination of their anatomy. The numerous defects, obscurities, and errors which a vain criticism might readily detect in his details under both of these heads, are justly attributable to the accident of position, for he was the first to track the road without the guide of a fixed nomenclature, and without the light which analogy could lend, anatomy at this period being scarcely practised, and physiology almost unknown.* By his own researches he was enabled to characterize several groups of Testacea, with some degree of precision, and to acquaint himself with many valuable particulars of their structure and economy, and although some of his general corollaries from these are hasty, yet even in this minor department of study the Stagyrite claims our admiration for his industry and sagacity, and our gratitude for giving us an example of scientific inquiry which it were well to follow.†

But the spring which welled so pure and copiously had no issue to its waters. Aristotle had no successor in testaceology among his countrymen: and when literature fled the shores of Attica, and found its unwilling way to Rome, it was unattended by the natural sciences. In the constitution

stature; so knowledge, while it is in aphorisms and observations, it is in growth: but when once is comprehended in exact methods, it may perchance be further polished and illustrated, and accommodated for use and practice; but it increaseth no more in bulk and substance."-Advanc. of Learning, p. 51. Duod. Pickering, 1840.-Also Sprengel, Hist. de la Médecine, i. 400.

"Tant d'eminens services rendus à l'anatomie comparée et à la zoologie, doivent lui faire pardonner quelques erreurs, dont les naturalistes du dixhuitième siècle, qui se font une gloire de rebaisser son mérite, ne sont pas même exempts."-SPRENGEL, Hist. de la Médecine, i. 398.

"Parmi les mollusques, Aristote désigne particulièrement la seiche, le calmar, le poulpe, l'argonaute, et fait remarquer, ce que l'on niait encore il y a peu de temps, que ce dernier animal n'est pas attaché à sa coquille comme les autres testacés. Il décrit sommairement tous les organes des mollusques, et mentionne même leur cerveau.”—CUVIER, Hist. des Sc. Nat. i. 150.—The labours of Aristotle have never been more generously or more highly appre ciated than by Cuvier, whose own knowledge entitled him to sit as the judge thereon. See the Hist. des Sc. Nat. i. 130, et seq. ; and the Edinb. New Phil. Journ. xxiii. 60-75.