CONCERNING TADPOLES 



189 



Breathing by means of the skin is practised by many of 

 the Amphibia : in the frog and toad, for instance, the skin 

 performs a certain amount of respiratory work, and during 

 the period of hibernation it is the sole means of breathing. 



The foregoing cases are further interesting as affording 

 yet other illustrations of the 

 fact we have already insisted 

 upon — the difficulty of draw- 

 ing any hard-and-fast Une 

 between embryonic and 

 post-embryonic characters ; 

 they show that, similarly, 

 there is no hard-and-fast 

 line to be drawn between 

 larval and adult characters ; 

 and we shall find further 

 and yet more striking in- 

 stances of these facts. 



Our survey of what we 

 may term the normal se- 

 quence of events in the 

 life-history of the frog tribe, 

 or to give the more technical 

 term, the Amphibia, is 

 ended. We are now to 

 pass in review some of the 

 more remarkable phases of 

 development which have, so to speak, been forced on 

 other members of this group by circumstances which we 

 can only roughly measure. These are all, as might be sur- 

 mised, exceptional cases, and confined to individual species, 

 and but for this ability to surmount the abnormal conditions 

 of existence imposed by their environment, that particular 



MEGALOPHRYS MONTANA. 



