PROGENITORS OF MAN. 289 
FouRrEENTH STAGE: Tailed Amphibians (Sozura). 
Our amphibious ancestors which retained their gills 
throughout life, were replaced at a later period by other 
Amphibia, which, by metamorphosis, lost the gills which 
they had possessed in early life, but retained the tail, as in 
the case of the salamanders and newts of the present day. 
(Compare p. 218.) They originated out of the gilled 
Amphibians by accustoming themselves in early life to 
breathe only through gills, and later in life only through 
lungs. They probably existed even in the second half 
of the primary, namely, during the Permian period, but 
possibly even during the Coal period. The proof of their 
existence lies in the fact that tailed Amphibians form a 
necessary intermediate link between the preceding and 
succeeding stages. 
FrrTEENTH Stace: Primeval Amniota (Protamnia). 
The name Protamnion we have given to the primary 
form of the three higher classes of Vertebrate animals, 
out of which the Proreptilia and the Promammalia developed 
as two diverging branches (p. 222). It originated out 
of unknown tailed Amphibia by the complete loss of the 
gills, by the formation of the amnion, of the cochlea, and 
of the round window in the auditory organ, and of the 
organs of tears. It probably originated in the beginning 
of the mesolithic or secondary period, perhaps even towards 
the end of the primary, in the Permian period. The 
certavn proof that it once existed lies in the comparative 
anatomy and the ontogeny of the Amniota.; for all Reptiles, 
Birds, and Mammals, including Man, agree in so many 
important characteristics that they must, with full assur- 
