TRANSITION TO THE AMPHIBIANS, 259 
respiratory organs of the Marsipobranchii with those 
of the amphibians,—it is possible that frogs and sala- 
manders may he 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 oldest amphibian-like animals, the 
Labyrinthodonts. From their remains (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 Ccecilia, which is how- 
ever without 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 
Ceecilia 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 
