ILLUSTRATIONS (6). PARASITIC TEBMES. 251 



( fc) p. 213 " Which inhabits the lungs of the Rattlcsnale of 

 the tropics. 1 " 



The animal which I formerly named an Echinorhynchvs, and 

 to which I even applied the term Porocephalus, appears, on a 

 closer inspection, according to Rudolphi's better grounded 

 opinion, to belong to the division of Pentastoma.* It is 

 found in the abdominal cavity and the wide-celled lungs of a 

 species of Crotalus, which, in Cumana, occasionally infests 

 even the interior of houses, and preys on mice. The Ascaris 

 lumbrici] lives beneath the skin of the common earth-worm, 

 and is the smallest of all the species of Ascaris. Leucophra 

 nodulata, Gleichen's pearl animalcule, has been observed by 

 Otto Friedrich Miiller in the interior of the reddish Nais lit- 

 toralis.'l It is probable that these microscopic animals are. 

 in their turn, inhabited by others. All are surrounded by air, 

 deficient in oxygen, and copiously charged with hydrogen and 

 carbonic acid. It is extremely doubtful whether any animal 

 could exist in pure nitrogen, although such an opinion did, 

 formerly indeed, seem warranted with reference to Fischer's 

 Cistidicola farionis, since, according to Fourcroy's experi- 

 ments, the swimming-bladder of fish was presumed to contain 

 air wholly devoid of oxygen. But the experiments made 

 by Erman, and confirmed by myself, prove that the 

 swimming-bladder of fresh-water fish never contains pure 

 nitrogen. In sea fish as much as 0'80 parts of oxygen have 

 been found, while, according to Biot's views, the purity of the 

 air depends on the depth at which the fishes live.|| 



(7) p. 214 " The united Lithophytes" 



According to Linnaeus and Ellis the calcareous Zoophytes, 

 (among which Madrepores, Meandrinae, Astrreae, and Pocil- 



ful development of mass and power of increase in the Infusorial animal- 

 cules, see Ehrenberg, In/us., s. xiii. 291 and 512. " The galaxy of the 

 smallest organisms," he says, " passes through the genera Monas (where 

 they are often only 3 J^ ; of a line), Vibrio, and Bacterium," (s. xix. 244.) 



* Rudolphi, Entozoorum Synopsis, pp. 124, 434. 



H- See Gb'zen's Eingeweidewurmer,^ tab. iv. fig. 10. 



J Miiller, Zoologia danica, Fasc. ii. tab. Ixxx. a e. 



Humboldt et Provencal, Sur la respiration des Poissons, in Rec* 

 d'Obs. de Zoologie, vol. ii. pp. 194216. 



|| Memoir es de Physique et de Cliimie de la Societt d'Arcueil, t 

 I 1807, pp. 252281. 



