372 CLASSIFICATIONS OF THE AMPHIBIA. 



that the whole function of the aquatic respiration in the ma- 

 nentibranchious amphibians is performed by the external 

 gills alone, but I conceive it to be not improbable that a por- 

 tion of it is aided, and in part effected, by the internal bran- 

 chial arcs themselves. The American authors 1 assert that 

 the Amphiuma and Menopoma have never been seen with 

 any external gills, but that the rest of the branchial appara- 

 tus remains unchanged throughout life ; unless then this ap- 

 paratus be superfluous or useless, (which I cannot suppose 

 at all likely), I think it more than probable that it performs 

 the part of real gills to those aquatic animals ; and that the 

 blood, in circulating through the branchial arteries, which 

 wind round and between those cartilages, becomes sufficient- 

 ly aerated by being submitted to the influence of the water 

 within the cervical apertures, and thus obtains the same ef- 

 fect or benefit, as if the respiration were carried on in the wa- 

 ter by means of them and external tufts conjointly, as in the 

 manentibranchians, or by the similar cartilages with their 

 pectinated and membranous appendages, as in the fishes. If 

 so, these two genera are correctly stationed in my diplopnen- 

 menous sub-class; and it is gratifying to learn that Mr. Hunter 

 held the like opinion, for he has included them, with the Si- 

 ren, 2 in his class which he termed Pneumobranchia. That 

 philosophical zootomist, in his ' General Observations 3 on the 

 Pneumobranchiata,'' has admirably stated his view of their 

 respiration in these two passages. — " This tribe of animals is 

 widely different from all hitherto known. They are com- 

 pounded of two grand divisions of the animal kingdom, yet 

 not so as for all their parts to partake equally of both ; for 

 some parts incline more to the one of these divisions, other 

 parts to the other, while a few are pretty distinctly made up 

 of both, so as to be truly double, just as the parts of gene- 

 ration are in perfect hermaphrodites, and these parts are the 

 organs of respiration, to which the circulation must of course 

 correspond. They hold with respect to respiration, a middle 

 rank between fish, which breathe water, and those immediate- 

 ly above them, which breathe air, viz., those called Amphibia 

 (Linn.), and they are placed in this respect between the two, 



1 See Dr. Garden's letter to Linnaeus in Smith's 'Correspondence,' vol. i. 

 p. 599. Also Dr. Harlan's paper in the Journal of the Acad. Nat. Sci. of 

 Philadelphia ; vol. iii. p. 54. cum tab. 1823 : and in Annals of the Lyceum 

 of Nat. Hist, of New York, pp. 223, 270, vol. i. 1824. 



2 With the respiratory organs of the Siren lacertina he was long acquaint- 

 ed, for that animal became one of his first subjects of comparative anatomy. 

 See his paper in the Phil. Trans, for the year 1706, p. 308. 



3 Now published in the Physiol. Cat. vol. ii. pp. 145 140. 



