[59] In the memoir on the Anatomy and Physiology of the Nematoids, by Dr. Charlton Bastian, which appeared in the Philosophical Transactions for 1866, we read that even these lowly organized worms have little power of repair. Speaking of the “paste eels” (Anguilulidæ), he says, “I may state as the result of many experiments with these that the power they possess of repairing injuries seems very low. I have cut off portions of the posterior extremity, and though I watched the animal for days after, could never recognize any attempt at repair.” Perhaps, however, the season may have some influence; and Dr. Williams’s denial respecting the Naïs may be thus explained. [What is said above was written in 1868, and published in the June number of the Fortnightly Review. In the August of that year the question of reproduction of lost limbs was treated by Prof. Rolleston in his Address to the British Medical Association, in which he showed cogent evidence for the conclusion that the reproduction of limbs only exists is animals that have feeble respiration, and consequently slow vital processes.]
[60] This beautiful and transparent larva reminds one in many respects of the Pike as it poises itself in the water awaiting its prey. It is enabled to do so without the slightest exertion by the air-bladders which it possesses in the two kidney-shaped rudiments of tracheæ, and which in the gnat become developed into the respiratory apparatus. The resemblance to the air-bladder of fishes is not simply that it serves a similar purpose of sustaining the body in the water, it is in both cases a rudiment of the respiratory apparatus, which in the fish never becomes developed. Weismann calls attention to an organ in the larvæ of certain insects (the Culicidæ), which have what he calls a tracheal gill, which gill has this striking analogy with the fish-gill that it separates the air from the water, and not, as a trachea, direct from the atmosphere. See his remarkable memoir Die nachembryonale Entwickelung des Muscidens, in Siebold und Kölliker’s Zeitschrift, 1864, p. 223.
[61] The Variation of Animals and Plants, 1868, II. p. 272.
[62] Origin of Species, 5th ed. p. 96.
[63] Mr. Darwin has himself, in the following passage, stated a somewhat similar view, and rejected it: “In one sense the conditions of life may be said not only to cause variability, but likewise to include Natural Selection, for the conditions determine whether this or that variety shall survive. But when man is the selecting agent, we clearly see that the two elements of change are distinct; the conditions cause the variability, the will of man acting either consciously or unconsciously accumulates the variations in certain directions, and this answers to the survival of the fittest under nature.” (p. 168.)
[64] Even in the nerve-sheaths of some Annelids there are muscles.
[65] Spencer, Principles of Biology, II. 72
[66] Faivre, Variabilité de l’Espèce, p. 15.
[67] These luminous organs would furnish an interesting digression if space permitted it. The student is referred to the chapter in Milne Edwards’s Leçons sur la Physiologie et l’Anatomie Comparée, 1863, VIII. 94, sq. Leydig, Histologie, 1857, p. 343. Kölliker, Microscopical Journal, 1858, VIII. 166, and Max Schultze, Archiv für mikros. Anat., 1865, p. 124. My friend Schultze was kind enough to show me some of his preparations of the organs of Lempyris splendidula, from which the drawings in his memoir were made. They reminded me of the electric organs in fishes by a certain faint analogy, the trachea in the one holding the position of nerves in the other. I may remark, in passing, that it is not every phosphorescent animal that has distinct luminous organs. There is a lizard (Pterodactylus Gecko) which occasionally becomes luminous. “A singular circumstance occurred to the colonial surgeon, who related it to me. He was lying awake in bed when a lizard fell from the ceiling upon the top of his mosquito-curtain; at the moment of touching it the lizard became brilliantly luminous, illuminating the objects in the neighborhood, much to the astonishment of the doctor.” Collingwood, Rambles of a Naturalist, 1868, p. 169.
[68] Max Schultze, Zur Kenntniss der electrischen Organe der Fische, 1858–9.