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Show 266 PHYSIOGNOMY OF PLANTS. that in living animals the evolution of light depends on an irritation of the nerves. I have seen an Elater noctilucus which was dying, emit strong flashes of light when I touched the ganglion of his fore leg with zinc and silver. Medusre sometimes show increased brightness at the moment of completing the galvanic circuit. (Humboldt, Rclat. Hist. t. i. pp. 79 and 533.) Respecting the wonderful development of mass and power of increase in Infusoria, see Ehrenberg, Infus. s. xiii. 291 and 512. He observes that 11 the galaxy of the minutest organisms passes through the genera of Vibrio and Bacterium, and that of l\lonas" (in the latter they are often only ~0J00 of a line), s. xix. and 244. ( 6) p. 230-" Which inhabits the large pulmona1:; cells of the rattler snalce of the t1·opics." This animal, which I formerly called an Echinorhynchus, or even a Porocephalus, appears on closer investigation, and according to the better-founded judgment of Rudolphi, to belong to the division of the Pentastones. (Rudolphi, Entozoorum Synopsis, pp. 124 and 434.) It inhabits the ventral cavities and wide-celled lungs of a species of Crotalus which lives in Cumana, sometimes in the interior of houses, where it pursues the mice. Ascaris lumbrici (Gozen's Eingeweidewiirmer, tab. iv. fig. 10) lives under the skin of the common earthworm, and is the smallest of all the species of Ascaris. Leucophra nodulata, Cleichen's pearl-animalculre, has been observed by Otto Friedrich M tiller in the interior of the reddish N ais littoralis. (Miiller, Zoologia danica, fasc. ii. tab. lxxx. a-e.) Probably these microscopic animals are again inhabited by others. All are surrounded by air poor in oxygen, and variously mixed with hydrogen and carbonic acid. Whether any animal can live in pu1·e nitrogen is very doubtful. It might formerly have been believed to be the case with Fischer's Cis.tidicoJa farionis, because according to Fourcroy's experiments the swimming bladders of fish appeared to contain an air entirely deprived of oxygen. Erman's experience and my own show, however, that fresh-water fishes never contain pure nitrogen in their swimming bladders. (Humboldt et Provengal, sur la respiration des Poissons, in the Recueil d'Observ. de Zoologie, vol. ii. pp. 194-216.) In sea-fish, as much as 0.80 of oxygen has been found, |