ON SOME ARMOURED FISHES. 
21 
important and sharply defined characters. . . . From Pisces , 
on the other hand, they are distinguishable only by the charac- 
ters of their locomotive apparatus. When they possess median 
fins and limbs, these never present fin-rays, and the limbs 
exhibit, in full development , the type of structure which 
obtains among the Sauropsida and Mammalia , and differ 
very widely from the fins of any fish at present known.”* 
He adds : f 66 With respect to the origin of the Amphibian 
stock itself, the following considerations appear to be of funda- 
mental importance : — The early stages of development of the 
Amphibia do not resemble those of any known ganoid, teleo- 
stean, or elasmobranch fish, and are similar to the correspond- 
ing stages of the Marsipobranchii , Myxine , Petromyzon .” 
“ The skull of the tadpole has much in common with that of 
Chimoera and with that of the Dipnoi , Geratodus , Lepido- 
sirenP “ The only Vertebrata , besides Amphibia , which have 
transitory external gills, are the Elasmobranchii ( Squalidce , 
Paiidce , Chimceridce ), the Dipnoi , and perhaps some ganoids.” 
“ The only fishes which possess morphological ( Polypterus ) or 
functional (Dipnoi) lungs are the ganoids and Dipnoi .” u The 
conclusions suggested by these facts appear to be that the 
Amphibia took their origin from some primordial form common 
to them, the Elasmobranchii , the Ganoidei , and the Dipnoi , 
and that the main distinction by which their earliest forms 
were marked off from those of the other groups was the develop- 
ment of that pentadactyle type of limb which is common to all 
the higher Vertebrata .” u And seeing that the elasmobranch, 
ganoid, and dipnoous types were fully differentiated from one 
another in the Devonian epoch, it is reasonable to believe that 
the existence of the Amphibia as a group dates hack at least 
as far as that remote period of the earth’s history.” 
As hearing upon this subject it is interesting to notice that 
among the remarkable assemblage of Beptilia from South 
Africa, lately described by Professor Owen, is a Dinosaurian 
Beptile ( Tapinocephalus Atherstoni ) in which my colleague 
Mr. Davies detected the curious fact that the vertebrae, like 
some fishes, have an amphiccelous form, being almost noto- 
chordal within, owing to the imperfect ossification of their 
centra. 
If the suggestions contained in the foregoing pages, as to the 
persistent notochord in early vertebrates, be of any genealogical 
or morphological value, then it may serve to indicate the 
earliest forms in each group, and even their relative develop- 
ment. 
* “ Encyclopaedia Britannica,” article Amphibia, Yol. i. 1875, p. 750. 
t Op. cit. p. 770. 
