STRUCTURAL DISTINCTIONS. 9 



"The pulmonic auricle," continues Sir Richard Owen, "thus 

 augments in size with the more exclusive share taken by the lungs 

 in respiration ; but the auricular part of the heart shows hardly 

 any outward sign of its diversion in the Batrachians. It is small 

 and smooth, and situated on the left, and in advance of the ventricle 

 in newts and salamanders. In frogs and toads the auricle is ap- 

 plied to the base of the ventricle, and to the back and side of the 

 aorta and its bulb." 



In the lower members of the order the single artery from the 

 ventricle sends, as in fishes, the whole of the blood primarily to the 

 branchial organs, and in all Batrachians at the earlier aquatic 

 periods of existence. In the Newt, three pairs of external gills are 

 developed at first as simple filaments, each with its capillary loop, 

 but speedily expanding, lengthening, and branching into lateral 

 processes, with corresponding looplets, these blood-channels inter- 

 communicating by a capillary network. The gill is covered by 

 ciliated scales, which change into non-ciliated cuticle shortly before 

 the gills are absorbed. In the Proteus anguinus, three parts only 

 of branchial and vascular arches are developed, corresponding with 

 the number of external gills. In Siren lacertina the gills are in 

 three pairs of branchial arches, the first and fourth fixed, the second 

 and third free, increasing in size according to their condition. 



Thus, the Amphibia have, at some stage of their existence, both 

 gills and lungs co-existent ; respiring by means of branchiae or gills 

 while in the water, and by lungs on emerging from it. 



All these creatures seem to have been well known to the 

 ancients. The monuments of the Egyptians abound in represen- 

 tations of Frogs, Toads, Tortoises, and Serpents. Aristotle was 

 well acquainted with their form, structure, and habits, even to 

 their reproduction. Pliny's description, however, presents some 

 amount of error and exaggeration. Their history is hid in darkness 

 during the Middle Ages, from which it gradually emerges in the 

 early part of the sixteenth century, when Belon and Rondeletius 

 in France, Salviani in Italy, and Gonrad Gesner in Switzerland, 

 devoted themselves to the study of natural history with great suc- 

 cess. In the latter part of the same century Aldrovandi appeared. 

 During fifty years he was engaged in collecting objects and making 

 drawings, which were published after his death, in 1640, being 

 edited by Professor Ambrosini, of Bologna, the reptiles forming 

 two volumes : in these volumes, twenty-two chapters are occupied 

 by the Serpents. But the first arrangement which can be called 

 systematic was that produced by John Ray, who based his system 

 75* 



