1880.] on ' The Origin of Sj^ecies: 365 



forms between birds and reptiles as the hypothesis required ever 

 existed '? And tlien probably followed a tirade upon this terrible 

 forsaking of the paths of " Baconian induction." 



But the progress of knowledge has justified Mr. Darwin to an 

 extent which could hardly have been anticipated. In 1862, the 

 specimen of Archcvoptcri/x, which until the last two or three years has 

 remained unique, was discovered ; and it is an animal which, in its 

 feathers and the greater part of its organization, is a veritable bird, 

 while in other parts it is as distinctly reptilian. 



In 18G8, I had the honour of bringing under your notice in this 

 theatre the results of investigations 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 conclusions 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 invertebrated animals, not only in their 

 structure, but, what was more important, in their development. I do 

 not think that we even yet know the precise links of connection 

 between the two; but the investigations of Kowalewsky and others 

 upon the development of AmpJtioxus and of the Tunicata prove 

 beyond a doubt that the differences which were supposed to constitute 

 a barrier between the two are non-existent. There is no longer any 

 difficulty in understanding how the vertebrate type may have arisen 

 from the invertebrate, though the full proof of the manner in which 

 the transition was actually effected may still be lacking. 



Again, in 1859, there appeared to be a no less sharp separation 

 between the two great groups of flowering and flowerless plants. It 

 is only subsequently that the series of remarkable investigations 

 inaugurated by Hofmeister has brought to light the extraordinary and 

 altogether unexpected modifications of the reproductive ajiparatus 

 in the Lycopodiacece, the Wdzocarpece, and the Gymnospermece, by 

 which the ferns and the mosses are gradually connected with the 

 Phanerogamic division of the vegetable world. 



So, again, it is only since 1859 that we have acquired that wealth 

 of knowledge of the lowest forms of life which demonstrates the 

 futility of any attempt to separate the lowest plants from the lowest 

 animals, and shows that the two kingdoms of living nature have a 

 common borderland which belongs to both or to neither. 



Thus it will be observed that the whole tendency of biological 



