« PreviousContinue »
framework, from which the flesh has disappeared. Certain species form coral only at their base or point of union. As the united polyps of a branch have their mouths opening outwards on every side, while their confluent bases are all directed inward towards a common central line, the secretion of coral by these bases necessarily produces a solid axis to the branch, which gradually indurates below as it grows from the apex, just like the branch of a tree. In this way is forined the horny stem of the Gorgonia, or sea-fan, so long deemed to be of vegetable origin, which, bereft of its polyps, as in our cabinet specimens, is like the branch of a shrub divested of its bark and foliage. The red or noble coral of the Mediterranean, — the Coral of the ancients and of the nursery, - is the calcareous axis of another species, stripped of its polyp exterior. Many of the shapes which the coral-forming zoöphytes assume are familiarly known.
“Madrepore shrubs and trees, and the sea-fan and other Gorgoniæ, from the West and East Indies, are common in collections. The hemispheres of brain-coral (Meandrina), and also of star-coral (Astræa), are often met with. It is very generally supposed, that these are by far the most frequent, if not the only shapes presented ; but, on the contrary, the varieties are extremely numerous, as we have already intimated. Some species grow up in the form of large leaves rolled around one another like an open cabbage, and cabbage-coral would be no inapt designation for such species. Another foliated kind consists of leaves more crisped and of more delicate texture, irregularly clustered ;lettuce-coral would be a significant name. Each leaf has a surface covered with polyp-flowers, and was formed by the growth and secretion of these polyps. Clustered leaves of the acanthus and oak are at once called to mind by other species; a sprouting asparagus-bed by others. The mushroom is here imitated in very many of its fantastic shapes, and other fungi, with mosses and lichens, add to the variety. The vases of flowers, to which allusion is made on a preceding page, are common about the reefs of the Pacific. They stand on a cylindrical base, which is enveloped in flowers when alive, and consist of a network of branches and branchlets, spreading gracefully from a centre, covered above with crowded sprigs of tinted polyps. The vases in the collections of the Expedition, at Washington, will bear out this description, although but the lifeless coral. The domes of Astræas are of perfect symmetry, and often grow to a diameter of ten or twelve feet without a blemish. The ruder hillocks of Porites are sometimes twenty feet across. Besides these, we might describe columns, Hercules' clubs, and various strange shapes which are like nothing but themselves." — pp. 59, 60.
Life, however, is but superficial in these masses. The present generations are building upon the tombs of their fathers. “An Astræa dome, twelve feet in diameter, although solid coral throughout, is alive for only half or three fourths of an inch from the surface"; and in the larger mounds of Porites, a thin living turf of less than half that thickness covers the remains of a myriad ancestry. The founders of the huge Astræas of the Red Sea, coeval at the least with the builders of the oldest pyramids, and the long line of their countless descendants, are thus all preserved together in an ever-increasing ossuary, forming their own mausoleum. The arborescent species are not only lifeless along the axis, but are dead throughout towards the bottom; as in a genealogical tree, only the ultimate ramifications are among the living. But the recent shoots Aourish with none the less luxuriance on a lifeless trunk, though death follows, æquo pulsat pede, leaving only a narrow interval. Life is but a span, at the best ; "the addition of an inch at the apex is death to an inch below.”
It is upon this principle of growing ever upward and onward, though perishing below, and upon the durability of the coral mass, protected by an ever active surface, that the power of these apparently insignificant animals to accomplish such great results depends. Themselves often microscopic in size, or but a few lines in height, they would otherwise be limited in their coral-making to a few inches at farthest, and merely incrust the surface upon which they grow, instead of constructing coral-reefs of vast extent, and in various ways bearing a most important part in the physical economy of the world. The extent of this agency, and the whole subject of coral-reefs, upon which it is understood that a large amount of important information has been gathered, our author has reserved for his forthcoming geological report. The physiological points of the subject, however, are admirably presented here. In his brief chapter upon the geographical distribution of zoöphytes, Mr. Dana informs us that the work is confided to different species or tribes in different zones or seas, and that each species, just as in the case of land animals and land plants, is generally confined to a comparatively narrow longitudinal range. The
range of the principal corals in depth, also, is remarkably restricted. “ Twenty, or perhaps sixteen, fathoms will include very nearly all the species of the Madrepore and Astræa tribes,” the principal reef-forming corals. A large part of our author's copious introduction - perhaps the most interesting one to the general naturalist - is devoted to showing how the almost infinitely various and singular forms, which different corals or compound zoöphytes present, arise from two or three fundamental modifications in the mode of budding, and the general plan of growth. Taking his cue from the vegetable kingdom, where it is easy to reduce the whole ramification to that particular plan according to which the whole development of the tree has taken place, from the primordial shoot to the ultimate branchlet and the latest leaf, Mr. Dana has ably and clearly shown, that all the forms of coral-structure are reducible to the same fundamental laws of organic growth. He has taught us, not only that the resulting shape of the coral strictly depends on the mode in which the successive polyps have from first to last budded and branched from the parent stem, but also that the actual modes in the zoöphyte are identical with those of vegetable growth. Each principal modification in the plant has its counterpart in the coralline vegetation. There is not merely an analogy between the two, but propagation and growth by budding are truly the same operation in both cases. The zóophyte is an animal which really grows like a plant. But, lest the subject should ramify beyond our narrow limits, we leave it abruptly, copying merely the closing paragraph of one of the author's most attractive chapters.
“ There is much to surprise and interest us in tracing out the simple causes of results so remarkable. The small polyp, incapable even of extending its arms without a drop of water to in. ject them, is enabled, by means of a simple secretion in its tex. ture, in connection with the process of budding, to rise from the rock and spread wide its branches, or erect, with solid masonry, the coral domes, in defiance of the waves that break over them. The microscopic germ of a Gorgonia developes a polyp barely visible to the naked eye, which has the power of producing a se. cretion from its base. The polyp buds, and finally the growing shrub is covered with branches and branchlets, many a mere thread in thickness, which stand and wave unhurt in the agitated waters. The same secretions fix it to its support, and so strong. ly, that even the rock comes away before the zoöphyte will break from its attachment. Tens of thousands of polyps cover the branches, like so many flowers, spreading their tinted petals in the genial sunshine, and quiet seas, but withdrawing when the clouds betoken a storm.
“A beautiful provision protects the branching coral-tree — often the work of ages - from being destroyed by the dissolving waters, when exposed, on the death and removal of the polyps. Certain minute incrusting corals — the Bryozoa and Sertularidæ, together with Nullipores — make the surface their resting-place, as soon as it is laid bare, and go on spreading and covering the dead trunk, and so prevent the wearing action of the sea. The Madrepore may thus continue to enlarge beyond its adult size ; the Caryophyllia may multiply almost endlessly its cylindrical branchings, although the living animal but tips the extremities of each ; for protection is given at once, when needed, and the polyps die, only to leave the surface to other forms of life, more varied and no less strange.
“ Finally, the coral becomes subservient to a still higher purpose than the support of polyps and nullipores. The debris, produced by the waves over a reef, settles into the many crevices among the dead trunks, and fills up the intervals, often large, between the scattered coral-patches; and, by this combined action of living growth and detritus accumulations, a solid rocky basement is formed, and kept in constant increase. In this way the coral-reef gradually nears the surface, and finally becomes the foundation of one of the fairest of
the sea-girt isles,
The unadorned bosom of the deep'; the coral polyps now yielding place to the flowers and groves of the land, which fulfil their end in promoting the comfort and happiness of man.” — pp. 83, 84.
Here, where our author rises from polyps to men, we may, with a good grace, take leave of him, and pass to the consideration of Mr. Hale's ethnographical and philological volume. But before doing so, we would briefly but most heartily commend the course which Mr. Dana has thought best to pursue in the principal systematic part of his work, where he has given a revision of all the coral-zoophytes (the Actinoidea) yet discovered ; rendering it, therefore, a complete manual, and the latest and fullest exponent of what is now known on this hitherto obscure and difficult subject. The propriety, not to say necessity, of this course will be evident to every one conversant with like subjects, when informed that two hundred and three out of the two hundred and sixty-one Actinoid zoöphytes collected in the cruise are here described for the first time, and that, of the four hundred and eightythree coral-zoöphytes described in the report (the Actiniæ, which make no coral, being excluded from this estimate), only two hundred and fifty-four, or little more than half, are to be found at all in previous works ; while even of those formerly known to naturalists, comparatively few had been examined in a living state. “It is, therefore,” to copy the modest statement in the preface, “no presumption on the part of the author, to say that a large amount of new information was obtained, nor a fact which might not have been anticipated, that such information has detected numerous errors in the received systems, or suggested changes of fundamental importance. In making out the report, it was found impossible, in many genera, to describe the newly discovered species without giving new and more definite characters to the old, and the genera themselves sometimes required a modification of their limits, and changes in their associations.”
A complete revision, therefore, by the light which the researches of the Expedition have thrown upon the whole subject, was probably the most compendious, and, beyond all question, the most desirable and useful plan. This plan Mr. Dana has accordingly adopted, and faithfully executed; producing a work upon one of the most curious and attractive, though formerly the most obscure and difficult, departments of the animal kingdom, which must long remain the standard authority upon the subject. Nor should it be forgotten, in our estimate of Mr. Dana's labors, that his scientific reputation hitherto has principally rested on his mineralogical writings, that the special field assigned to him was the geology of the Expedition, upon which his reports are still to be made, and that it was only in the course of the voyage, owing to the withdrawal of a zealous member of the scientific corps to whom this department was originally consigned, that the subject of zoöphytes fell into his able hands.
The work of Mr. Hale will do credit both to himself and to the country. As this is his first appearance, we believe, in the capacity of an author, it will be proper that we introduce him to our readers. Mr. Hale is the son of Mrs. Sarah J. Hale, well known as a writer and as the editor of a popu