v.] THE COMMON FROG. 53 



To what existing animals can these huge monsters 

 be considered to have affinity ? It is impossible to 

 say that they in any way bridge over the chasm 

 separating the Frogs from the Efts. They appear 

 indeed to have been almost equally removed from 

 both — for the possession of short limbs and a long 

 tail (characters common to so many widely different 

 animals) cannot be regarded as any good evidence of 

 affinity. 



It is not improbable that they find their nearest 

 allies in the existing insignificant OpJiioniorpha. The 

 latter, though apparently naked, have minute scales 

 imbedded in the skin and arranged in rings at 

 intervals, and the skull is provided with certain extra 

 ossifications. The Labyrinthodonts have similar 

 extra, cranial ossifications, and though they have not 

 rings of scales, the ventral region was protected by 

 minute plates arranged in linear series converging in- 

 wards and forwards towards the middle line. More- 

 over, some forms appear to have been entirely devoid 

 of limbs ; at least no remnant of such parts has yet 

 been discovered. Nevertheless the degree of develop- 

 ment of the tail constitutes a marked distinction 

 between the LabyrintJiodonta and the Ophioino7pha. 



Certain Labyrinthodonts had great formidable 

 teeth in elongated jaws like"^ those of crocodiles. 

 Altogether these singular remains tempt us to specu- 

 late as to the succession of life upon this planet's 

 surface. We know that as to the later secondary 

 period that part in the life of the globe which is 

 now played by beasts was then played by reptiles 

 Instead of the existing bats, Pterodactyles of all 



