- [Footnote: belong to the division of the Pentastomes. (Rudolphi,
Entozoorum Synopsis, p. 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 (Gözen's Eingeweidewürmer, Tab. iv. Fig. 10,) lives under the skin of the common earthworm, and is the smallest of all the species of Ascaris. Leucophra nodulata, Gleichen's pearl-animalcule, has been observed by Otto Friedrich Müller in the interior of the reddish Nais littoralis. (Müller, 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 pure nitrogen is very doubtful. It might formerly have been believed to be the case with Fischer's Cistidicola 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 shew, however, that fresh-water fishes never contain pure nitrogen in their swimming bladders. (Humboldt et Provençal, sur la respiration des Poissons, in the Recueil d'Observ. de Zoologie, Vol. ii. p. 194-216.) In sea-fish as much as 0·80 of oxygen has been found, and according to Biot the purity of the air would appear to depend on the depth at which the fish live. (Mémoires de Physique et de Chimie de la Societé d'Arcueil, T. i. 1807, p. 252-281.)]
