vu “THE ORIGIN OF SPECIES ” 935 
years, has remained unique, was discovered ; and 
it is an animal which, in its feathers and the 
greater part of its organisation, is a veritable 
bird, while, in other parts, it is as distinctly 
reptilian. 
In 1868, I had the honour of bringing under 
your notice, in this theatre, the results of investi- 
gations made, up to that time, into the anatomical 
characters of certain ancient reptiles, which 
showed the nature of the modifications in virtue 
of which the type of the quadrupedal reptile 
passed into that of a bipedal bird; and abundant 
confirmatory evidence of the justice of the con- 
clusions which I then laid before you has since 
come to light. 
In 1875, the discovery of the toothed birds of 
the cretaceous formation in North America by 
Professor Marsh completed the series of transitional 
forms between birds and reptiles, and removed 
Mr. Darwin’s proposition that “many animal 
forms of life have been utterly lost, through 
‘which the early progenitors of birds were 
formerly connected with the early progenitors of 
the other vertebrate classes,’ from the region 
of hypothesis to that of demonstrable fact. 
In 1859, there appeared to be a very sharp 
and clear hiatus between vertebrated and inverte- 
brated animals, not only in their structure, but, 
what was more important, in their development. 
T do not think that we even yet know the precise 
