IV FUNCTIONAL ADAPTATION 165 



when it has peeled, by elevations on its surface, which are 

 called "pearls." The antler very often has an extremely 

 long pearl on the internal side of the main stem. In one of six- 

 points it is between the lowest branch and the base. This 

 structure is obviously the commencement of a new branch in 

 process of evolution, for it is occasionally as much as an inch 

 long, and then has all the appearance of a new branch, 

 and " may be counted as such in venery." ^ 



In this we have therefore an instance of the oris^in of a 

 new part of an organ by simple growth. 



Only in this gradual way, by the inheritance of acquired 

 modifications sometimes together with degeneration, number- 

 less organs in the animal body can have been evolved. Con- 

 sider the limbs of Ungulata and other animals : the foot of 

 the horse, of the ostrich, the hind -foot of the kangaroo, in 

 their partly degenerate, partly specialised structure, depend 

 only upon inherited acquirements due to adaptation to the 

 same physiological demand, i.e. diminution of the number of 

 the toes, and increase in strength of the one or few remaining for 

 the sake of greater firmness and more rapid progress on hard 

 ground — in contrast, for example, with the five-toed foot of the 

 elephant, which is adapted to prevent any sinking into the soil. 



The treatment of comparative anatomy, especially of 

 osteology, from this physiological point of view, which at 

 present, to my regret, has almost entirely fallen into disuse, 

 has its own special attractions, and affords at every point 

 support to my views. In this respect so-called analogous 

 organs are of the utmost importance — organs which, although 

 occurring in very different animals not immediately allied by 

 descent, have a very similar form, because they serve the 

 same purpose ; thus, for instance, the similarity in the forma- 

 tion of the limbs in the cases just mentioned, the development 



^ Cf. J. H. ^^%m%, Naturgesckichte cler Sdugethiere Deutschlands, 1857, s. 464. 



