CLASSIFICATIONS OF THE AMPHIBIA. 377 



the greater part of them, although in their adult state terres- 

 trial animals, are in the habit of resorting to lakes, ponds, and 

 other fluviatile places, and are capable of remaining under 

 the water x for a considerable length of time, without rising to 

 the surface in order to inhale atmospheric air. In this sense, 

 then, it is, that we must confine the signification of ampliibi- 

 ous, as almost universally made use of; and certainly it is to 

 be so translated in the following lines of the very ancient 

 poet j — 



A'(ji<pi@iov ya$ spooks vo/xm Ba,T()ctx 0l<Tl KfowW, 

 X)ti%TYi<Tai Korea, ynv, kou hep 1 ti^acri crajxa JtaXv-^ai. 



Homeri Batrach. v. 59. 



(For we, amphibious), " by gift from Jove," 

 (Do) " leap as well as swim, can range the land 

 " For food, or diving, seek it in the deep." 



Cowper : Trans, v. 79. 



Now, whether this power of remaining long submerged 

 under water, without performing the function of respiration, 

 arises from the cold blood in these animals, when first suffi- 

 ciently aerated, being able to continue its slow circulation for 

 a considerable time together ; or, from the lungs having the 

 capacity of retaining such a quantity of air, as to permit the 

 circulation to go on uninterruptedly, for a long period ; or, 

 from the circulation being in some degree earned on indepen- 

 dently of the lungs ; because, in these amphibians, the blood 

 is only in part passed through the lungs and so aerated, while 

 the other part circulates again from the heart, through the 

 rest of the body, independent of transmission through the pul- 

 monary organs ; or from the pulmonary vessels being so small 

 as to allow the respiration to be suspended, without stopping 

 the circulation of the blood ; or from whatsoever organic 

 cause 2 it may be considered to be effected, I will leave ana- 



x Many of the monopneumenous adult amphibians are admirably adapted 

 to an aquatic life, in having some of their organs protected against injury 

 from the water, and in having others so formed as to be of material assist- 

 ance to them, when diving in that element. Of the former are, the nostrils, 

 (through which alone many sorts breathe), which are often furnished with 

 small valves, to prevent both the entrance of water, and the escape of the 

 air inhaled for respiration ; the ears are usually covered by a membrane, and 

 the eyes are defended by two, or even three, eyelids : of the latter, are, the 

 crystalline lenses in the eyes of some kinds, which assume a more spherical 

 shape, approaching to those in fishes, the toes of the hind feet are frequently 

 webbed, and the tails, sometimes being compressed, greatly aid in swimming. 



2 1 have not made any allusion to a third mode of respiration, with which 

 some of these animals are endowed ; namely, that of breathing water, or at- 

 mospheric air, by means of their skin; because, how far this cutaneous re- 

 spiration is really possessed by, or of actual service to, the different groups 

 of the Amphibia, is as yet unknown. 



