TRANSFORMATION OF ORGANS OF ANIMALS 59 



The hand of the oldest known bird, however, 

 Archceopteryx had only three digits, and the 

 question arises as to whether this atrophy of the 

 two outer digits was effected in the process of 

 the animal's gradual adaptation to flight or if it 

 dates from a still earlier period. 



Archceopteryx had four toes. The fore legs were 

 smaller than the hind legs. Now, with bipedal or 

 quadrupedal animals which make no special use 

 of their fore legs, the contrary may invariably be 

 noticed. It is of small importance, therefore, 

 whether Archceopteryx was quadrupedal or bipedal 

 before it took to flying, for neither of these modes 

 of progression would have entailed the loss of two of 

 its digits, and the disappearance may reasonably be at- 

 tributed as due to the process of adaptation to flight. 



The three remaining digits of Archceopteryx were 

 complete in their structure. The phalanges, which 

 were of different lengths, are furnished with claws, 

 and were of the same number as is normal among 

 reptiles, i.e. 2, 3, 4, counted from the inner side. 

 The wing of Archceopteryx had not therefore under- 

 gone much modification beyond the toes of the two 

 outer digits, but it must be remembered that the 

 bird was a weak flyer ; instead of having a large 

 boney sternum necessary for powerful flight, the 

 sternum of Archceopteryx was formed of cartilage, 

 and the wings were short and rounded in shape. 



With good flyers, on the other hand such as 

 pigeons or sea-birds the adaptation to flight is 



