CLASSIFICATIONS OF THE AMPHIBIA. 369 



In this order I have divided the animals into four families, 

 characterized by the shape of their body when adult, their 

 tailless form, the presence of a long tail, &c. 



I must here observe, that although the adult caducibran- 

 chians may be well ascertained and correctly specified, we 

 know little of the exact varieties of form assumed and chang- 

 ed by the larvae of each species ; to describe indeed the tad- 

 poles of one or two species of any of the genera of that order, 

 otherwise than the supposed general appearance of those of 

 all the species, is clearly incorrect ; for careful investigations 

 have only been made on the tadpoles of the common frog, the 

 edible frog, the toad, the aquatic salamander, 1 and probably 

 a very few other species, but of the greater number of those 

 of the more rare and foreign kinds, we are at present quite 

 ignorant. So likewise we know nothing of the very first ap- 

 pearance of the immature animals, — I mean especially when 

 first produced from the ova, — belonging to the latter, or Am- 

 phibia Diplopneumena, which are supposed never to trans- 

 form ; concerning them, I expect, Zoology will some day re- 

 ceive many curious facts. 



The second sub -class, or diplopneumenous kinds of amphi- 

 bians, are those which respire by the aid of a double breathing 

 apparatus, namely, by lungs and by gills, or gill-like organs, 

 both of which the animals simultaneously retain during the 

 whole period of their life. So that consequently the circula- 



processes or lobes of the external branchice, turning round the tips or extre- 

 mities, and ascending up the opposite side. The blood continues to circu- 

 late with great velocity, and in a regular and continued stream. This 

 phenomenon struck me as one of the most beautiful I ever beheld. 



1 Those who wish to pay attention to this subject, and " mutatas dicere 

 formas" of the different larva, I refer to the three following beautifully-il- 

 lustrated monographs by Dr. Rusconi, as examples worthy of their imita- 

 tion. — ' Descrizione Anatomica degli organi della circolazione delle Larvae 

 delle Salamandre Acquatiche:' con tavola : 1817. 'Amoures des Salaman- 

 dres Aquatiques, et developpement du tetard de ces Salamandres depuis 1' 

 ceuf jusqu' a l'animal parfait.' 1821 . ' Developpement de la Grenouille 

 commune, depuis le moment de sa naissance jusqu' a son etat parfait.' — 

 1826. And see Humboldt and Bonpland's Voyage, vol. i. part 2 plate 13$ 

 for Cuvier's illustrations of the tadpoles of Bufo fuscus and Salamandra 

 aquatica. Sir E. Home also published in the ' Phil. Trans.' for 1825, p. 

 81, a paper " On the changes the ovum of the Frog undergoes during the 

 formation of the Tadpole," illustrated by accurate and beautiful plates 

 from the pencil of Bauer ; but he has neglected to give a representation of 

 the singular mode in which the external branchice are often seen to disap- 

 pear, about the sixth or seventh day from the birth. On one side the little 

 creatures (in some specimens) exhibit at that age no appearance of exter- 

 nal tufts ; and on the other side, only the extremities of these tufts are vi- 

 sible, being nearly drawn urithin the cervical aperture. 



