CHAPTER IV 
CONNECTING LINKS 
THE supply of connecting links can never equal the 
demand. The discovery of the Ornithorhyncus brought 
to light a connecting link between mammals on the 
one side and birds and reptiles on the other. It lays 
eggs ; it has a beak like a bird’s ; its anatomy is highly 
reptilian, and it suckles its young. Geology shows us 
an animal, evidently akin to the Horse, with four 
toes, and thus we are able to put the Horse down 
as a near relation of the Rhinoceros and the Tapir. 
But the mending of one gap does not prevent the 
existence of others. It often seems even to call 
attention to them. Remains of extinct animals have 
been found which certainly to some extent bridge the 
gulf between birds and reptiles. Such evidence of 
relationship is very valuable, but it is easy to mistake 
its nature. These fossil reptiles, in so many ways 
birdlike, must not be looked upon as the ancestors of 
birds. Nor do they, like the Ornithorhyncus, carry us 
back to a low unspecialised type. They are only con- 
necting links in this sense, that they show that some 
undoubted reptiles much resemble birds, that reptiles 
