Page:Popular Science Monthly Volume 6.djvu/172

160 what a strange, brush-like appendage! That fleshy pad is its locomotive organ; and a very funny, but quite pretty contrivance it is. The projected pad is encircled by a frill of cilia, or fleshy hairs, arranged much as the frill is around the large pin-cushion which occupies a place before the mirror of a lady's boudoir. As these cilia play together, the illusion is produced of a revolving wheel; and, in fact, it is the uni-cycle velocipede of this baby-voyager, with which it must do some traveling in quest of a home, or permanent settlement for life. This frilled organ can be projected and withdrawn in rapid alternations. While being projected, the circular frill expands, thus achieving a very efficient propulsion. And, while being withdrawn, it contracts, or is involved within itself, in this way presenting the least possible resistance to the water. This mechanism, as I understand it, is as remarkable as it is beautiful. It fulfills perfectly, or certainly to a remarkable degree, the conditions of perhaps the most perplexing of the unsolved practical problems in naval science—the attainment in union of the maximum power of propulsion and the minimum resistance from back-water.

If we examine a snail, or conch, as typical of the univalve mollusks, or shell-fish, we shall find the organs of sense, mouth, tentacles, and eyes, so arranged together as to entitle the object to be known as a cephalate mollusk, that is, one which has a head. The bivalves are not so highly organized, and are acephalate, or headless. It is a curious fact, however, that in the larval state many of these bivalves have eyes, though they lose them as growth proceeds. Although we think it probable, it has not yet been proved, that the larval oyster has eyes. To witness the merry high time of these juveniles, it would seem that they both have eyes and are bound to use them, too, in seeing something of the world; for, as if eviction entailed neither disgrace nor inconvenience—as with certain bipedal juveniles under pupilage—off they go in the wildest glee imaginable. But the gay frolic is soon over. A few settle down, like the old folks, to a sober life. Alas! it is with the rollicking young oysters as with many other young people—this wild-oat sowing yields a fruitful but perilous harvest. Of each million that enter upon this dissipation, but a few hundreds, at the most, survive. Many have been devoured by hungry enemies lying in wait, and many went to sea, and, unable to return, perished miserably. The survivors attach themselves to any thing that offers an anchorage; and these are called "spat." Fig. 1 contains five groups of oysters of as many different ages, all of which, by a professional oysterman, would be called "spat," excepting the three largest at the top. The attachment is made at the lower valve. And, now having wound up its giddy career, what was done with the velocipede? In plainer words, what is to become of the locomotive pad, for which it has no further use? It begins to disappear—not by atrophy, however, nor is it sloughed off in any way. Herein appears