30 ANIMAL LIFE PAST AND PRESENT. 



after the manner of the feathers on an arrow. It will, 

 however, be readily imagined that such a long unwieldy 

 tail was by no means calculated to act as an efficient 

 and compact rudder ; and the shortened tails of modern 

 birds appear, therefore, to be a decided improvement 

 on the early type. It seems, indeed, that in all groups 

 of Vertebrates capable of true flight a long tail has 

 been found disadvantageous, since among the Ptero- 

 dactyles the more specialised kinds found in Europe 

 had discarded the long tail of the species represented 

 in Fig. 11 ; and the same holds good with regard to the 

 large toothless kinds found in the Cretaceous rocks of 

 the United States. Again, the most specialised, or 

 insectivorous Bats are remarkable for the shortness of 

 their tails. From the relative shortness of its wings, 

 coupled with the long unwieldy tail, it is probable that 

 the Archseopteryx was but a poor flyer, and was, 

 perhaps, altogether incapable of making the long- 

 sustained flights of our modern birds, though it must 

 undoubtedly have been a true flyer. 



Birds vary greatly in the relative proportions of the 

 component bones of the wing, so that among the 

 strongest flyers we find that whereas in the giant Alba- 

 tross of the tropical seas the bones of both the upper 

 and fore-arm are enormously elongated, in the Swift 

 that of the upper arm is so shortened and thickened as 

 to be scarcely recognisable. The form and arrange- 

 ment of the flight-feathers are, however, of still greater 

 importance in modifying the shape of the wing, but 

 the reader desirous of information on this subject must 



