250 



VERTEBUATE ANIMALS. 



Toads, aud in somu others, there are two sets of gills, one external 

 and the other internal, of which the former is soonest lost. The 

 Inngs of the AiniJjibians never attain a very high state of develop- 

 ment ; and in tliose forms in wliich the gills are retained throughont 

 life, the chief business of res|>iratio:i appears to lie carrieil on by the 

 gills. In accordance with the changes in the respiratozy pmce.ss, 

 corresponding alterations take jilace in the blood-vessels. With the 

 development of the lungs the vessels which carry blood to them (the 

 nulmonary arteries) increase in sirre, whilst the branchial vessels, 

 which cany the bhjod to the gills, undergo a proj)ortii:jnate diminu- 

 tion. At iii.st the condition of the circulation is very much the 

 same as it is in lishes, but ultinjately it becomes nearly the same as 

 in the true Keptiles. 



The Ainphihia are divi.led intii 

 as follows ; — 



three livini; and one extinct order 



( IRUFR I. (JrniOMORPIIA. 



This order is an extremely small fine, and, as its name implies, it 

 comprises certain snake-liice Amphibians. The order includes onlj' 

 the curious animals known as Ccecilue (tig. 180), which ai'e found in 



Fi,;. ISO. -(J Sii,lin„ni,, .mualuliit. ,,i f lln; Orriliaiis 



sa ; .; .Muiilli, sl.nniim tlir Imi-nr, I,,.,. Ill, I in 



(/ Tail rif tin; siiiiie. ( All I'l' Dmurril ar,a nil.nni.) 



■il ; '. ll.'ii.l .if th.^ 

 ^s .il' 111,. Hiislrils; 



Southern Asia, Afiica, and South Auierica. Tlie body is entirely 

 ili'stiliite of limbs, .'111(1 is eiicliiseil in an integunieiit wliich is thrown 

 iiitc nimicioiis transverse wrinkles, and srimetimes has miuierous 



