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 



