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these tracks reveal is, that, at the commencement of the Meso- 
zoic epoch, bipedal animals existed which had the feet of birds, 
and walked in the same erect or semi-erect fashion. These 
bipeds were either birds or reptiles, or more probably both ; 
and it can hardly be doubted that a lithographic slate of Triassic 
age would yield birds so much more reptilian than ArchceopteryXy 
and reptiles so much more ornithic than Compsognathus, as 
to obliterate completely the gap which they still leave between 
reptiles and birds. 
But if, on tracing the forms of animal life back in time, we 
meet, as a matter of fact, with reptiles which depart from the 
general type to become bird-like, until it is by no mean5 
difficult to imagine a creature completely intermediate between 
Dromceus and Compsognathus, surely there is nothing very 
wild or illegitimate in the hypothesis that the phylum^ or genea- 
logical tree, of the class Aves has its root in the Dinosaurian 
reptiles ; that these, passing through a series of such modifica- 
tions as are exhibited in one of their phases by Compsognathus , 
have given rise to the Ratitce ; while the Carinatce are still fur- 
ther modifications and differentiations of these last, attaining 
their highest specialisation in the existing world in the Pen- 
guins, the Cormorants, the Birds of Prey, the Parrots, and the 
Song-birds. 
However, as many completely differentiated birds in all pro- 
bability existed even in the Triassic epoch, and as we possess 
hardly any knowledge of the terrestrial reptiles of that period, 
it may be regarded as certain that we have no knowledge of 
the animals which linked Beptiles and Birds together historically 
and genetically ; and that the Dinosauria, with Gompsogna-- 
thus, Archceopteryx, and the Struthious Birds, only help us to 
form a reasonable conception of what these intermediate forms 
may have been. 
In conclusion, I think I have shown cause for the assertion 
that the facts of Palaeontology, so far as Birds and Eeptiles are 
concerned, are not opposed to the doctrine of Evolution, but, 
on the contrary, are quite such as that doctrine would lead us to 
expect; for they enable us to form a conception of the manner 
in which Birds may have been evolved from Eeptiles, and thereby 
justify us in maintaining the superiority of the hypothesis, that 
Birds have been so originated, to all hypotheses which are 
devoid of an equivalent basis of fact. 
