576 GENERAL .CHARACTERS OF BATRACHIA. 



519. The respiration of these animals is effected, as already 

 stated, by means of lungs in the mature state ; but as the ribs are 

 wanting, it is evident that the air cannot be drawn in and ex- 

 pelled by a series of inspirations and expirations, in the same 

 way as in the higher Yertebrata. We find accordingly that, as 

 in the Tortoises, in which the ribs, although present, have no 

 power of motion, the air is passed into the lungs by a movement 

 of deglutition. The respiration is exceedingly sluggish, especi- 

 ally in cold weather ; in warm weather it is far more active. A 

 Frog, for example, which has been deprived of air, perishes in 

 summer in less than two hours, whilst in winter it may continue 

 to live for several days. A considerable amount of cutaneous 

 respiration also appears to go on in these creatures, and during 

 the winter this seems to be sufficient for the maintenance of 

 their existence ; in winter the lungs of a Frog may be removed 

 without producing asphyxia, whilst in summer they have need 

 riot only of the pulmonary respiration, but also of the cutaneous, 

 and death soon occurs when the air does not act upon the skin, 

 or is excluded from the lungs. Limitation of the supply of air 

 often produces in these animals a lethargic dulness, analogous to 

 that of hybernating animals. 



520. Like the Reptiles, the Batrachia are all oviparous, and 

 in most cases the eggs are not impregnated by the male until 

 after they have quitted the body of the female. The eggs are 

 usually deposited in the water, even by those species which pass 

 the greater part of their lives on land ; they are enveloped in a 

 glutinous matter, which unites them into large masses or long 

 chains ; the latter looking like necklaces of black beads. The 

 masses of eggs of the common Frog may be constantly seen in 

 the spring floating upon the water frequented by these animals. 

 These eggs are remarkable as being those in which the entrance 

 of the spermatozoa into the yolk was first seen by the late Mr. 

 Newport. 



521. But it is in the mode of development that we find the 

 most striking difference between the Batrachia and the true 

 Reptiles. Both are produced from eggs; but in the Batra- 

 chia the young are not evolved in the form which they ultimately 



