" The physiologist perceives at every step, proofs of design which baffle human comprehension, but the ideas they raise are vague and undefined, and so, of course, the application too is indistinct ; but when we can, from first to last, perceive the end in view, and understand the means of its accomplishment, the mind is satisfied, and owns at once how great the foresight and how grand the power of the Supreme Designer.
" The crust of the Bchinus, when denuded of its spines, and stripped of its external coverings, would seem to be an ordinary shell, having its outer surface covered over with polished tuber cles, regularly arranged. Of these the largest are disposed in lines that pass from pole to pole of the round box, like lines of longitude upon the globe of the geographer.
" Intermixed among the larger tubercles are seen innumerable smaller eminences of similar construction, but dispersed with less precise arrangement, upon all of which, when in a living state, spines were attached in corresponding number. Moreover, placed at intervals between the spine-crowned tubercles are ten broad bands, disposed in pairs, all pierced with countless holes ; these too extend from pole to pole of the round box, and through them, during life, the locomotive suckers passed, already noticed as being used for climbing rocks or for attachment to some foreign body. On cutting through the shell, so as to see its inner surface, we perceive, to our surprise, that far from being, as it appears externally, a simple shelly exudation moulded to the form of the Echinus like the shells of lobsters or mollusca, it is a very complex fabric built with most consummate art, con sisting of some thousand pieces varying in size, but shaped with mathematical precision, and conjured with so much accuracy, that the eye can but with difficulty trace the line of union. Tell a human artisan, however versed in geometrical proportions, to cut out a thousand plates, polygonal in form, and fit them to each other, leaving not the slightest space between their margins any where, so that the whole shall form a hollow sphere of certain given proportions, how would he succeed ? Doubtless he would pronounce the problem quite impracticable. But in the shell before us, that is what nature has achieved most perfectly.
First, we observe five double rows of oblong plates, pentagonal in form, which on their outer sides present the spine-supporting tubercles. On either side are found innumerable pieces of a smaller size, but equally exact in shape, through which are bored the perforations for the ambulacral feet, and these again are separated from another row of perforated plates by other inter mediate pieces having spines affixed externally. These plates are mostly pentagons in form, with sides of various lengths, but all combined, fit each other so closely, that their combination seems to form one solid, compact shell.
" We shall not stop to count the number of the plates com prised in every series, or to calculate how many perforations are provided for the feet. Let the reader try to number them when opportunity occurs, though here, numbers are of little consr quence. Let us rather ask why Nature in this case has chosen to work by laws so complex, when we might suppose a simpler fabric might have done as well ? why frame a shell composed of thou sands of small portions thus connected, when even in higher animals all this elaborate device can be dispensed with ? A little thought will convince us that, even here as elsewhere, Nature has employed no useless superfluity of structure. To case the animal in stone, would have been a simple process ; as we have already seen that almost all the zoophytes secrete calcareous matter in abundance ; but, when thus closed up in a stony shell, how could the creature grow ? Here is the difficulty. We might as well expect a Chinese lady's foot to grow while shod in iron, as that an Echinus should expand from the small size it first presents, to its adult dimensions, without some remarkable pro vision being made to allow of such an increase. Growth con stantly goes on, and yet the crust itself, being, when once formed, devoid of life, and as incapable of growing as if made of marble, cannot expand as do the bones of higher animals, neither is any part left soft, but at all ages, the whole shell has the same com pactness and solidity throughout, and presents the same precise distinctive form peculiar to the species. The only way in which this difficulty could be met is, obviously, that which Nature has adopted.