[70] Fritz Müller first demonstrated a nervous system in the Polyzoa:—“The nervous system of each branch consisting of—1st, a considerable sized ganglion situated at its origin; 2nd, of a nervous trunk running the entire length of the branch, at the upper part of which it subdivides into branches, going to the ganglia of the internodes arising at this part; and 3rd, of a rich nervous plexus resting on the trunk, and connecting the ganglia just mentioned, as well as the basal ganglia of the individual polypides.” For further account, see paper in the “Micros. Journ.,” vol. i., New Series, p. 330.
[71] I have ventured to devote some considerable space to the development of the pond-snail, and for an obvious reason, that of making it perfectly clear to my readers that my microscopical investigations of Limnœa, made in 1853, were published in the “Journal of the Microscopical Society,” June, 1854, and republished in extenso in the several editions of this book, dating from the last mentioned period. Nevertheless, the fringe of cilia was, it appears, rediscovered in 1874, just twenty years after my paper was published. It is almost unnecessary to add that Carpenter gravely errs in his statement “that the existence of the fringe of cilia in the embryo snail had been overlooked until 1874.”
[72] Mr. George Rainey many years ago made us acquainted with the fact that certain of the appearances presented by the shell or other hard structures of animals, and which had hitherto been referred to as cell-development, are really governed by the physical laws which govern the aggregation of certain crystalline salts when exposed to the action of vegetable and animal substances in a state of solution. Mr. Rainey furnished a process for obtaining artificially a crystalline substance which shall so closely resemble shell structure that it can barely be distinguished from it. The chemical substances to be used in the preparation of the artificial shell, or calculi, are a soluble compound of lime and carbonate of potash or soda, dissolved in separate portions of water, and mixed with some viscid vegetable or animal substance, as gum or albumen, and mixing the several solutions together. The mechanical conditions required are that such a quantity of each of the viscid materials in each solution shall be of about the same density as that of the nascent carbonate of lime, and at perfect rest. This state of rest will require from two to three weeks or longer. Mr. Rainey shows the analogy or identity of his artificially formed crystals with those found in natural products both in animals and vegetables, chiefly confining himself to the structure and formation of shells and bone, pigmental and other cells, and the structure and development of the crystalline lenses, which he contends are all formed upon precisely the same physical principles as the artificial crystals.
[73] E. Ray Lankester, “On the Gregarinæ found in the common Earthworm.”—“Micros. Trans.” vol. iii. p. 83.
[74] For the fullest information of marine, land, and fresh-water species, consult Dr. Bastian’s “Monograph on the Anguillulidæ”; “Lin. Soc. Trans.” vol. xxv. p. 75; the “Anguillula Aceti,” by the author, in the “Popular Science Review,” January, 1863.
[75] “Cercaria parasitic on Limnœa,” “Jour. Royal Micros. Soc.” 1870.
[76] See my paper “The Natural History of a Nematode Worm,” “Journ. of Microscopy and Natural History,” October, 1888.
[77] “The Parasites of Man and the Diseases which proceed from them,” by Professor Rudolf Leuckart, 1886.
[78] R. J. Pocock, “On Worms” (Warne, Op. cit.), p. 465.
[79] An interesting account of the formation of the tubes of Serpula is given by Mr. Watson, “Jour. Micros. Soc.,” vol. 1890, p. 685.