Page:Hardwicke's Science-Gossip - Volume 1.pdf/116

100 A POPULAR DESCRIPTION OF POLYCYSTINS.

HILST engaged in 1861 and 1862 in delineating the microscopic forms in some of the Barbadoes earths brought to England by Dr. Davy, and beautifully prepared for the microscope by Mr. Johnson, of Lancaster, the progress of my interesting occupation being partially watched by the late

accomplished Dr. Boott, he exclaimed, "You surely have found the excavated toilette-service of Titania, with all her essence-bottles and trinkets." Yes, in that dirty-looking, chalky earth are indeed found exquisitely jewelled vases, and diamond crosses and stars, to represent in fairy miniature the badges of every order of knighthood. But what, then, are these Polycystins? They are a family of the Rhizopods; the type of which group, and the object most attainable for examination, is the amœba, which may so frequently be found in the sediment of fresh-water streams or pools, or even in the moss of damp garden-walks, or similar situations, like drops of a translucent jelly, each drop having within it, though only discernible to practised microscopic eyes, a speck, an atom, which physiologists term the nucleus, and suppose it to be the first germ or commencement of animal life in its lowest form. The enveloping jelly is called sarcode, and differs but slightly from the cellulose of low vegetable forms of life. The little lump or globule of sarcode is self-coherent, though it is supposed to have no outer skin or integument to hold it together; and if watched under a lens, it will be seen to shoot out small portions like fingers, or as they are called pseudopodia (false feet), with which it has the power of creeping along in its native element; nay, more wonderful still, it can seize with them any small infusoria or alga, frequently some small diatom, which it can completely suck into, and bury in its own substance, melting out, as it were, all the nutritious part for its own sustenance, and then throwing the useless débris to the outside of the mass of sarcode. "Here, then, we have,"—as Dr. Carpenter so eloquently expresses it,—"living substances in which vital operations are carried on without any special instruments whatever; a little particle of apparently homogeneous jelly, changing itself into a greater variety of forms than the fabled Proteus, laying hold of its food without members, swallowing it without a mouth, digesting it without a stomach, appropriating its nutritious material without absorbent vessels or a circulating system, moving from place to place without muscles, feeling (if it has any power to do so) without nerves; and not only this, but in many instances forming shelly coverings of a symmetry and complexity not surpassed by those of any testaceous animals."

Now, the Polycystins are lumps of sarcode; and it is precisely this power of constructing shelly coverings which attracts our notice to them. They actually do spin or weave for themselves coverings resembling the most delicate and costly silver filagree-work, rivalling in pattern the choicest productions of the ancient Peruvians or modern Easterns. Yet, our little Polycystin artificers choose a far more beautiful material than silver, being a shining transparent preparation of silex, which these little lumps of apparently inert jelly possess,—a cunning laboratory capable of extracting the silex from the sea-water and fitting it for use. But it is not only outer-corselets that they construct, there are also solid internal pillars and rafters to support and strengthen the fabric, in the exterior walls of which suitable and convenient open spaces are carefully left for the extrusion of the pseudopodia, which we may suppose are sent out in all directions to collect and bring home whatever is needful, either for nourishment or for continuing their work. The internal supports so much resemble the nature of the spiculæ of sponges, as to bring the polycystins and sponges into very near relationship, although they belong to distinct groups of the family of Rhizopods. As yet so few naturalists have observed the Polycystins in a living state, that their history seems hardly determined. Dr. Wallich has in store a mass of valuable information, which he has not yet given to the public. Among the most diligent, careful, and successful observers of these organisms was the late Professor Johannes Müller, who fished them up in quantities from their native habitats on the sea-bed, under the clearest and purest sea-water of the Mediterranean, near St. Tropez and Cette. But