CLASSIFICATIONS OF THE AMPHIBIA. 373 



filling up the scale." "An animal to be truly amphibious, 



must have its respiratory apparatus compounded of the pul- 

 monary and branchial organs, which is the case with this 

 tribe, for these only can be said, when in the air, to be truly 

 terrestrial, and when in the water truly aquatic." 



Having before shown that the circulating organs are, in 

 these two genera, both strictly pulmonary and branchial ; 

 and of these, the latter perhaps most prevail, for on either side 

 of the aorta, three branchial arteries proceed to the gill-like 

 parts, whilst only one artery descends upon each lung, and 

 this organization is said to continue unaltered during the 

 entire life of the animals ; wherefore, it is almost naturally 

 certain, that the respiration itself, like the corresponding cir- 

 culation, is also two-fold, — both branchial or aquatic, and 

 pulmonary or atmospheric. Again, by comparing these organs 

 with those of the caducibranchians, or such animals as under- 

 go a metamorphosis, for example, with those of the water sala- 

 mander, we see that the branchial arteries proceed in the 

 same course x in the young or tadpole, when its respiration is 

 entirely aquatic ; but when the lungs are fully developed, 

 the pulmonary arteries are prepared for action, and when the 

 gill apparatus is decayed, all the branchial arteries (except 

 two) with their branches become obliterated, and the two re- 

 maining (formerly branchial) arteries unite into one at the 

 back, and send off a branch directly to the lung ; 2 and since 

 the gills, the arcs, the apertures, and opercles, in the adult 

 become quite evanescent, the two arteries (branchial) can no 

 longer be of any service in aquatic respiration, for they are not 

 exposed to, or in anywise influenced by, the water. The en- 

 tire respiration is ever afterwards effected by the lungs alone 

 in the atmosphere. But it has been already explained that 

 the branchial arteries continue, in the Amphiuma and Meno- 

 poma, always to wind round and between the permanent arcs 

 or gill-like organs, and to expose the blood contained within 

 them to the water, either passing through the cervical open- 

 ings, or therein retained by the closing of the persistent lids ; 

 thus do they differ in a most essential way from the final con- 

 dition of the similar parts in the mature salamander, 2 and in 



1 This may be well seen on referring to the plates in Rusconi's 'Amours 

 des Salamandres,' and to plate 13, part 2, vol. i. Voyage de Humboldt. 



2 Cuvier correctly writes, — " dans les especes qui perdent leurs branchies, 

 les rameaux qui s'y rendent s'obliterent, excepte deux, qui se reunissent 

 en une artere dorsale, et qui donnent chacun une petite branche au pou- 

 mon. — C'est une circulation de poisson metamOrphosee en une circulation 

 de reptile." — Regne Animal, tome ii. p. 102. 



3 Compare fig. 6, representing this adult animal anatomically displayed, 



