VIII 



INHERITED MODIFICATIONS 



the foot (see Fig. 4), it will be seen that the first digit or 

 hallux is entirely wanting, but the other four 

 toes are present with their complete number of 

 phalanges. The fourth is immensely developed, 

 the fifth moderately so, but the second and 

 third are reduced to the most slender rudi- 

 ments, and are so united in life by a common 

 integument, that they look like a single toe 

 with a double claw. 



Now, here are two feet as unlike as possible 

 in their functions the one formed for rapidly 

 hopping along over the arid plains, the other 

 for slowly and securely climbing among the 

 boughs of the forests yet presenting a deep- 

 seated resemblance in a character not found in 

 the feet of any other known mammal except 

 the immediate allies of these two. 



We may call this " conformity to type " 

 without getting much nearer to an explanation 

 of the phenomenon. Perhaps it is safest to 

 rest at this stage. 



But is it not powerfully suggestive I will 

 not say more, for, of course, by itself it cannot 

 be considered as a proof of true relationship, 

 of inheritance from a common ancestor ? We 

 can easily see that in some manner the great 

 preponderance of the one toe in the kangaroo, 

 and the reduction^ of the others, would be 

 advantageous in its mode of progression, reduc- e an s aro < 



cropus major). 



ing the foot to a narrow spring-board as it 

 were ; and we can see that this attenuation of the second and 

 third toes, after the first had quite disappeared, might be a 

 stage in the direction of their total disappearance. But while 

 this was taking place, let us suppose that one branch of the 

 family took to climbing trees (I must not enter fully into all 

 that might be supposed on this subject, as I am merely 

 introducing this as an example of the mode in which morpho- 

 logical problems are illustrated by these general views), and 

 the variations in a particular direction, tending towards better 



I 



FIG. 4. Skeleton 

 of the hind foot of 



