TRANSITION TO THE AMPHIBIANS. 259 



respiratory organs of the IMarsIpobranchii with those 

 of the amphibians, — it is possible that frogs and sala- 

 manders may be directly descended from beings closely 

 analogous to the division of the Marsipobranchii termed 

 Myxine. It is to be hoped that this highly interesting 

 observation may soon be made public. We gather 

 from the general Ontogenesis of the amphibians, that 

 the tailed forms are the most ancient. This is also 

 the case with the eldest amphibian-like animals, the 

 Labyrinthodont.«. From their reniains (Archegosaurus 

 and others), chiefly contained in the Carboniferous for- 

 mation, we have learnt that they had incomplete limbs 

 or none, that their ventral side was partially provided 

 with bony plates, the vertebral column fish-like, and 

 that their skull, with some of the characters of the 

 present amphibians, combined others which remind us 

 partly of certain bony Ganoids, and partly of the 

 reptiles which subsequently appeared. Now if in the 

 singularly elongated snake-like Coecilia, which is how- 

 ever v/ithout tail or limbs, some peculiarities of the 

 skull of the Labyrinthodont appear again, we must 

 own our utter ignorance as to the actual progenitors of 

 this, as well as of the two other living orders of the 

 Coecilia and the Batrachians. Here, therefore, we are, 

 as we have said, thrown entirely on the evolutionary 

 history of the individual. By what right we may 

 frame a picture with great probability approaching the 

 truth, the reader may have gathered from our previous 

 chapters. 



Among the tailed amphibians, it is not only in 

 Ontogenesis that we see the passage from gill to lung- 

 breathing ; the systematic series from the proteus to 

 the triton and the salamander, likewise exhibits this 



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