Page:Popular Science Monthly Volume 9.djvu/572

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The lakes to which we have devoted the greatest attention, and which are at the same time the most common and the most interesting, are those which fill glacier-worn rock-basins, to which we hope that, our little article will attract the attention of some one who will give us more light on these wonderful pictures, now but imperfectly illuminated.



IN the swamps of the Gambia, after they have been dried by the tropical sun, there are to be found here and there beneath the surface clods of earth uniform in shape, and usually about the size of a man's two fists. These clods inclose living animals, which have been led by instinct to hide themselves away toward the close of the rainy season, and before the coming of the season of drought, by burying themselves in the mud while it was yet soft, and before it had been hardened by the scorching rays of the sun.

On breaking one of these lumps of mud, it is found to be a sort of pouch or cocoon, with thin walls, and with projections here and there corresponding to the form of the animal concealed within. Its larger end is rounded, but its narrower end is closed by a slightly convex lid with a narrow opening in the centre. If the surface of the cocoon be even gently touched, a pretty loud cry is heard which Natterer has compared to the mewing of a cat.

For a long time it was supposed that the animal buried itself amid the leaves which surround its protecting sheath. In a special memoir published in the Bulletins of the St. Petersburg Academy of Sciences, Leuckart expressed the opinion that the epidermis, by becoming detached, supplied the materials for this envelope. But since his time it has been demonstrated that the cocoon is formed from a dense secretion of mucus; such is the result of observations made by Paulson and Richard Owen, and repeated by Auguste Duméril, Professor of Ichthyology at the Museum. He has himself witnessed the formation of the cocoon, and his description of the process we repeat here in his own words. He says:

"Two protopteri, that had been restored to freedom by the gradual softening of the clods in which they had been inclosed, evinced signs, after living for a month in an aquarium, that the time had come for them to seek, in the soft earth covered by the water, the shelter which they require during the dry season. Their restlessness, their abundant secretion of mucus, their attempts at burrowing, all showed an irresistible desire to find a medium different from that in which they then lived.
  1. Translated from the French, by J. Fitzgerald, A.M.