266 



THE DOCTRINE OF DESCENT. 



the discoveries, scanty as they are, of fossil intermediate 

 forms. The pelvis and leg of the Ornithoscelidae have 



already been discussed. But in the 

 slates of Solnhofen we have more- 

 over become acquainted with the 

 Archseopteryx, a bird unfortu- 

 nately mutilated and in many 

 ways damaged by pressure (Fig. 

 25, impression of the tail of the 

 Archaeopteryx Macrurus, Ow), but 

 exhibiting a very valuable and 

 interesting intermediate stage be- 

 tween the tail of a reptile and a 

 bird. Among existing birds, the 

 Nandu, or American ostrich (Rhea), 

 alone possesses numerous separate 

 caudal vertebrae ; but the tail of 

 this bird projects so little, that it 

 in no way recalls the tail of a lizard. 

 Now the Archaeopteryx exhibits a 

 long tail, bordered by two rows 

 of stiff feathers, of which the 

 impression remains in extraordinary preservation. The 

 skull of this valuable specimen, now in the British 

 Museum, is so much injured, that no idea can be framed 

 of its construction. It is impossible to decide whether 

 the jaw^s bore teeth. The example of the tortoises 

 shows that within the reptile type the formation of teeth 

 was replaced by horny sheaths, without a correlated 

 development of the power of flight ; the Pterodactyles, 

 on the other hand, combine with the power of flight a 

 light head, provided nevertheless with numerous teeth. 



FIG. 



