Rudiments. 55 



existence, speed, either in escape or pursuit, must always have proved 

 a winning quality, and consequently a subject of selection. Those ani- 

 mals which raise themselves off their heels and run on their toes, in- 

 crease the length of their legs and consequently their speed. The 

 changes brought on by the adaptive stimulation of the environment and 

 natural selection, gradually raised the heel higher and higher, and at the 

 same time brought (he longer middle toes into more exclusive use, de- 

 veloping them excessively, and tending to abolish the shorter outside 

 ones by depriving them of functional activity. Fig. 69 shows the loss 

 of one digit, the thumb, in the case of the pig, while two others, the 

 2nd and 5th, are of no use and have become too short to touch the 

 ground. The ox has lost his thumb. His index and his little finger 

 are reduced to little rudiments which hang on behind, and he walks on 

 his middle finger and "ring finger." The horse has lost all except the 

 middle finger. The metacarpal bones which formerly supported his in- 

 dex and ring fingers, have long been useless and have almost disap- 

 peared, too, but a splinter on each side of the middle carpal bone still 

 remains as their representative. See further on the histcwy of the horse, 

 in chapter 13. 



In the genus Jin I is of the lizzard f amity, there are no fore limbs, and 

 consequently no use for the shoulder bones. It has, however, rudi- 

 ments of cartilage, representing the shoulder blade and collar bone, 

 also a useless cartilaginous breast bone, which does not articulate with 

 any ribs. This animal has inherited these relics of members which 

 were in use amongst its remote ancestors, but which the changed habits 

 of his immediate ancestors and himself have rendered useless. Other 

 snake-like lizzards, as the blind worm (anguis) and the sheltopusik, are 

 reduced in the same way. 



Squirrels have five toes in the hind but only four in the fore feet 

 with an additional tubercle representing the thumb. They hold their 

 nuts between these tubercles when gnawing. 



The sharks and rays possess rudiments of the air bladder, showing 

 their ancestors, the early selachians, to have had it. 



Darwin remarks: "rudimentary organs may be compared with the 

 letters in a word, still retained in the spelling but become useless in the 

 pronunciation, but which serve for a clew in seeking for its derivation. " 



As we go on we shall have occasion to point out numerous additional 

 examples of retrograde adaptation and persistent rudiments, the relics 

 of old time organs now long gone out of fashion. 



