HERPETOLOGY. 453 



The Amphibia, at an early stage of their existence, are fur- 

 nished with gills, and, like fishes, respire in water; the gills, indue 

 time, become obliterated, and lungs developed, as in the frog, 

 the newt, &c., (Plate XIII.) Others, however, of this group, 

 though they acquire lungs, never lose their gills, and are at the 

 same time both aquatic and aerial in their respiration, or capa- 

 ble of breathing both in air and water. Such are the Proteus, 

 the Siren, and the Axolotl. The former are called Caduci- 

 branchiate, (Lat. caducus, falling or perishable; branchia, gills ;) 

 the latter are termed Perennibranchiate, (Lat. perennis, durable ; 

 branchia, gills.) In the latter Amphibians, the ventricle receives 

 blood from the auricles, and transmits it into an enlarged arte- 

 rial vessel or bulb, which soon divides into separate branches, 

 one being destined for each leaf of the gills essentially like those 

 of a fish ; here these arterial vessels sub-divide into five capil- 

 laries, and these at length, (as in fishes,) gradually pass into 

 branchial veins which at last emerge into two vessels, and these 

 unite to form the aorta, or great arterial trunk. Into this aorta, 

 the blood purified in the gills, or branchiae, is conveyed without 

 being first sent back to the heart; and from this aorta, it is dis- 

 tributed throughout the system. But besides the branchial, these 

 Amphibians have also a pulmonic, (Lat. pulmo, a lung,) circula- 

 tion. By the pulmonary artery proceeding from the aorta, a 

 portion of the blood which has already been partially oxygenated 

 in the gills, is conveyed to the lungs, where it is still further 

 purified. It is then sent through pulmonic veins to the left auri- 

 cle, and from that to the ventricle, whence, mixing with the vitia- 

 ted blood of the system, it is sent to the gills, and thence to the 

 aorta, from which a portion again passes to the lungs, the rest to 

 the system, and so on in a perpetual succession. 



The Caducibranchiates, at the commencement of their exist- 

 ence, have only gills truly developed, and the circulation is bran- 

 chial or fish. like. The lungs are, at this period, in a rudimen- 

 tary state, and the pulmonary arteries exceedingly minute. In 

 process of time, however, a new impetus is given to the pulmo- 

 nary arteries and to the lungs, at the expense of the branchial 

 arteries and the gills ; as the former develop, the latter decrease, 

 until at the last, the branchial apparatus entirely perishes, no 

 trace of it being left; while certain vessels, which formed a 

 junction" bet ween the branchial system of arteries and the pulmo- 

 nic arteries, enlarge, and now add only to the pulmonic circula- 

 tion. Thus the circulation in the frog and newt changes, by a 

 wonderful transition, from that of a fish to that of a perfect rep- 

 tile ! while in the Proteus and its allies, it continues to be that 



