Page:Popular Science Monthly Volume 19.djvu/241

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229
THE PRIMEVAL AMERICAN CONTINENT.

which pass through an essentially similar development, there is no stalk; and the animal, after its free-swimming stage, simply glues its head, by a kind of marine cement of its own manufacture, to the rock, develops its conical shell, and like the barnacle uses its modified feet as means for exercising the commissariat and nutritive function. It is true that in some respects the adult barnacle may be regarded as lower than the young, and therefore as a degenerate being. Thus, it is lower when eyes, feelers, and movements are taken into account. In other respects the adult may be considered of higher organization than the larva. These higher traits we may logically enough suppose represent the special advances which adult barnacle-life has made on its own account. But, on the whole, degradation and retrogression, if not so fully exemplified as in the sacculina, is still plainly enough illustrated in barnacle history. When we further reflect that even such high crustaceans as prawns and allied forms begin life each as a "nauplius" or under an allied guise, we not only merely discover the common origin of all crustaceans in some form represented by the "nauplius" of to-day, but we also witness the possibilities of development which have placed shrimps, prawns, etc., in the foremost rank of the class, and which, conversely, have left the barnacles and sacculinas, through the action of degenerative changes, among the groundlings of the group.

The assumption of a sedentary life, whether parasitic in nature like that of sacculina, or whether it is represented by mere attachment and fixation to some inorganic thing, as in the case of the barnacles, is therefore seen to operate in the direction of producing degeneration of the animal's constitution. The tendency of such habit is toward simplification of structure and not toward that progressive advance and evolution which, in the case of the higher crustacean races, have evolved from the relatively simple "nauplius" of the past the crabs, lobsters, shrimps, and prawns of to-day.—Gentleman's Magazine.

[To he continued.]

 
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THE PRIMEVAL AMERICAN CONTINENT.
By L. P. GRATACAP, A. M.

THE reader may recall standing, when a child, by the side of a toy-dam in the course of some little stream, and, were a breach made in the mimic masonry, remember the mute interest with which he watched the slow emergence of fairy islands as points of rock and shoals of mud slowly appeared above the water's surface—how the detached summits, at first round spots, assumed varied outlines indented with cones or bristling with promontories; how they multiplied as the ebbing water exposed newer and lower levels, until the