I trust I have succeeded in showing that the three Orders of the Acalephs are, like the five Orders of the Echinoderms, different degrees of complication of the same structure. In the Hydroids, the organization does not rise above the simple digestive cavity inclosed by the double body-wall; and we might not suspect their relation to the Acalephs, did we not see the Jelly-Fish born from the Hydroid stock. In the Hydroid-Medusae and Discophorae, instead of a simple digestive sac, as in the Hydroids, we have a cavity sending off tubes toward the periphery, which ramify more or less in their course. Now whether there are four tubes or eight, whether they ramify extensively or not, whether there are more or less complicated appendages around the margin or the mouth, makes no difference in the essential structure of these bodies. They are all disk-like in outline, they all have tentacles hanging from the margin, and a central cavity from which tubes diverge that divide the body into a certain number of portions, bearing in all the same relation to each other and to the central cavity. In the Ctenophorae, another complication of structure is introduced in the combination of vertical with horizontal tubes and the external appendages accompanying them.
But, whatever their differences may be, a very slight effort of the imagination only is needed to transform any one of these forms into any other. Reverse the position of any simple Hydra, so that the tentacles hang down from the margin, and let four tubes radiate from the central cavity to the periphery, and we have the lowest form of Jelly-Fish. Expand the cup of the Hydra to form a gelatinous disk, increase the number of tubes, complicate their ramifications, let eyes be developed along the margin, add some external appendages, and we have the Discophore. Elongate the disk in order to give the body an oval form, diminish the number of main tubes, and let them give off vertical as well as horizontal branches, and we have the Ctenophore.
In the Class of Polyps there are but two Orders,—the Actinoids and the Halcyonoids; and I have already said so much of the structure of Polyps that I think I need not repeat my remarks here in order to show the relation between these groups. The body of all Polyps consists of a sac divided into chambers by vertical partitions, and having a wreath of hollow tentacles around the summit, each one of which opens into one of the chambers. The greater complication of these parts and their limitation in definite numbers constitute the characters upon which their superiority or inferiority of structure is based. Here the comparison is easily made; it is simply the complication and number of identical parts that make the difference between the Orders. The Actinoids stand lowest from the simple character and indefinite increase of these parts; while the Halcyonoids, with their eight lobed tentacles, corresponding to the same number of internal divisions, are placed above them.
We have the key-note to the common structure of the three Classes whose Orders we have been comparing in the name of the division to which they all belong: they are Radiates. The idea of radiation lies at the foundation of all these animals, whatever be their form or substance. Whether stony, like the Corals, or soft, like the Sea-Anemone, or gelatinous and transparent, like the Jelly-Fish, or hard and brittle, like the Sea-Urchins,—whether round or oblong or cylindrical or stellate, in all, the internal structure obeys this law of radiation.
Not only is this true in a general way, but the comparison may be traced in all the details. One may ask how the narrow radiating tubes of the Acalephs, traversing the gelatinous mass of the body, can be compared to the wide radiating chambers of the Polyp; and yet nothing is more simple than to thicken the partitions in the Polyps so much as to narrow the chambers between them, till they form narrow alleys instead of wide spaces, and then we have the tubes of the Jelly-Fish. In the Jelly-Fish there is a circular tube around the margin into which all the radiating tubes open. What have we to compare with this in the Polyps? The outer edge of each partition in the Polyp is pierced by a hole near the margin. Of course when the partition is thickened, this hole, remaining open, becomes a tube; for what is a tube but an elongated hole? The comparison of the Acalephs with the Echinoderms is still easier, for they both have tubes; but in the latter the tubes are inclosed in walls of their own, instead of traversing the mass of the body, as in Acalephs, etc.
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In preparing these articles on the homologies of Radiates, I have felt the difficulty of divesting my subject of the technicalities which cling to all scientific results, until they are woven into the tissue of our every-day knowledge and assume the familiar garb of our common intellectual property. When the forms of animals are as familiar to children as their A, B, C, and the intelligent study of Natural History, from the objects themselves, and not from text-books alone, is introduced into all our schools, we shall have popular names for things that can now only be approached with a certain professional stateliness on account of their technical nomenclature. The best result of such familiarity with Nature will be the recognition of an intellectual unity holding together all the various forms of life as parts of one Creative Conception.
GABRIEL'S DEFEAT.
In exploring among dusty files of newspapers for the true records of Denmark Vesey and Nat Turner, I have caught occasional glimpses of a plot perhaps more wide in its outlines than that of either, which has lain obscure in the darkness of half a century, traceable only in the political events which dated from it, and the utter incorrectness of the scanty traditions which assumed to preserve it. And though researches in public libraries have only proved to me how rapidly the materials for American history are vanishing,—since not one of our great institutions possesses, for instance, a file of any Southern newspaper of the year 1800,—yet the little which I have gained may have an interest which makes it worth preserving. I have never been able to see why American historians should be driven to foreign lands for subjects, when our own nation has furnished tyrannies more terrible than that of Philip of Spain, and heroes more silent than William of Orange,—or why our novelists must seek themes in Italy, on the theory avowed by one of the most gifted of their number, that this country is given over to a "broad commonplace prosperity," and harbors "no picturesque or gloomy wrong." But since, as the Spanish proverb says, no man can at the same time ring the bells and walk in the procession, so it has perhaps happened that those most qualified to record the romance of slave-institutions have been thus far too busy in dealing with the reality.
Three times, at intervals of thirty years, has a wave of unutterable terror swept across the Old Dominion, bringing thoughts of agony to every Virginian master, and of vague hope to every Virginian slave. Each time has one man's name become a spell of dismay and a symbol of deliverance. Each time has that name eclipsed its predecessor, while recalling it for a moment to fresher memory: John Brown revived the story of Nat Turner, as in his day Nat Turner recalled the vaster schemes of Gabriel.