BIRDS 379 



any bird sees is due to our invention of instruments, 

 supplementing by lenses the imperfections of our eyes. 

 In addition to the peculiarities of the eye itself, birds 

 have a sort of extra eyelid, the nictitating membrane, 

 which when drawn across the eye shades it from intense 

 light. This structure is present, more or less devel- 

 oped, in many other vertebrates. 



7. In any classification of birds, the Arch&opteryx Primitive 

 stands quite apart. Although extinct many millions 

 of years ago, it is known by two wonderfully preserved 

 fossils, from the Upper Jurassic rocks of Solenhofen in 

 Bavaria. Not only are the forms of the bones clearly 

 indicated, but the impression of the feathers on the 

 rock remains. The creature is described as of about 

 the size of a crow, with a small head having toothed 

 jaws and no true beak. The neck vertebrae were less 

 numerous than in modern birds. The tail was most 

 remarkable, with about twenty bones as in a reptile, 

 but covered with long feathers. There were birdlike 

 wings, with long feathers adapted for flight, but these 

 wings had in addition three digits, each with a hooked 

 claw. The legs were four-toed. This animal was 

 certainly a member of the class Aves, since it had 

 feathers ; but in other respects it was intermediate 

 between birds and reptiles. It is almost the ideal 

 "link" which evolutionists might have postulated and 

 hoped to find. Other toothed birds, called Hesper- 

 ornis and Ichthyornis, have been found in the Creta- 

 ceous rocks of Kansas. These are not only more recent 

 than the Archceopteryx, but are much more like typical 

 birds. 



8. Many other extinct birds are known, though the The great 

 remains are mostly fragmentary. From the Lower 

 Eocene of Wyoming comes the gigantic Diatryma, 



