220 THE HISTORY OF CREATION, 
opposed to all other Vertebrate animals which breathed 
through gills (Branchiata). In all the Vertebrata already 
discussed, we found that they either always breathed 
through gills, or at least did so in early life, as in the 
case of Frogs and Salamanders. On the other hand, we 
never meet with a Reptile, Bird, or Mammal which at any 
period of its existence breathes through gills, and the gill- 
arches and openings which do exist in the embryos, are, 
during the course of the ontogeny, changed into entirely 
different structures, viz. into parts of the jaw-apparatus and 
the organ of hearing. (Compare above, vol. i. p. 307.) All 
Amnionate animals have a so-called cochlea in the organ of 
hearing, and a “round window” corresponding with it. These 
parts are wanting in the Amnion-less animals; moreover, their 
skull lies in a straight line with the axis of the vertebral 
column. In Amnioticanimals the base of the skull appears 
bent in on the abdominal side, so that the head sinks upon 
the breast. (Plate IIT. Fig. C,D,G,H.) The organs of tears 
at the side of the eye also first develop in the Amniota. 
The question now is, When did this important advance 
take place in the course of the organic history of the earth ? 
When did the common ancestor of all Amniota develop out 
of a branch of the Non-amniota, to wit, out of the branch of 
the Amphibia ? 
To this question, the fossil remains of Vertebrata do 
not give us a very definite, but still they do give an 
approximate, answer. For with the exception of two 
lizard-like animals found in the Permian system (the 
Proterosaurus and Rhopalodon), all the fossil remains of 
Amniota, as yet known, belong to the secondary, tertiary, 
and quaternary epochs. With regard to the two Vertebrata 
