3()8 CLASSIFICATIONS OF THE AMPHIBIA. 



effected by means of a single breathing- apparatus ; that is to 

 say, either altogether by lungs alone, or else at first by gills 

 and then by lungs. 



This sub-class includes the first and second orders. The 

 first order gives the abranchians, viz., such animals as are 

 never found to be furnished with gills at any time of their 

 existence ; wherefore they always breathe atmospheric air, 

 and the consequent circulation of the blood is, of course, 

 merely pulmonary. There is only one family in this order, 

 — the CcBciliadce; which naturally constitute a link interme- 

 diate between, and allied to, both the ophidians and the true 

 amphibians : to the former they are similar in their external 

 forms, in having neither legs nor gills, and from their second 

 lung r being much smaller than the first ; to the latter they 

 approach in the smallness and shortness of their ribs, and in 

 the formation of their hyoid bones, from the appearance of 

 which one might be induced to suspect that some branchial 

 apparatus once existed, and that a metamorphosis had actu- 

 ally taken place. 



The second order embraces all those animals which (as 

 yet are known to) undergo any metamorphosis : these are the 

 frogs, the frog-like amphibians, and the family of salamanders. 

 In their early forms, larvae or tadpole stages, they breathe by 

 gills in the water, just as fishes do ; and after their transfor- 

 mations, or in their perfect state, they respire simply by the 

 aid of lungs in the atmosphere. Hence, the term ' Caduci- 

 branchia ' sufficiently points out as well the phenomena ex- 

 hibited by the changes in the forms of this natural group, as 

 their most singular qualities, — of first respiring in water by 

 gills, which, when they have performed their service to the 

 immature creatures, become obliterated, or decay, together 

 with their cartilaginous arcs and deciduous lids or opercula ; 

 —and of afterwards respiring in air by proper and fully-de- 

 veloped lungs. 2 And the circulation of the blood in the one 

 case would be branchial, 1 but in the other only pulmonary. 



1 Cuvier observes, " leur deuxieme poumon est aussi petit que dans les 

 autres serpens." — 'Regne Animal,' tomeii. p. 99. 



2 Les batraciens "ont tous deux poumons egaux, auxquels se joignent, 

 dans le premier age, des branchies qui ont quelque rapport avec celles des 

 poissons, et que portent aux deux cotes du col des arceaux cartilagineux, 

 qui tiennent a 1' os hyoide. La plupart perdent ces branchies et P appareil 

 qui les supporte, en arrivant a Petat parfait." — Cuvier; ' Regne An. tome 

 ii. p. 101. 



3 The circulation through the external branchial tufts of the young tad- 

 poles of the common frog, when only three or four days old, affords a very 

 interesting object for the microscope. The globules of blood may be seen 

 passing, in a distinct current, down one side of the transparent finger-like 



