2 6o PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



But the two palm bones to which they were attached 

 still remain as useless splints to attest the original 

 three-toed condition. These and other changes are 

 shown in diagram, Fig. 165. {b) In ruminants the toes 

 are reduced to two, but we have already shown (page 

 253) that useless remnants of the other two are still 

 found in most ruminants, showing their original four-toed 

 condition. (<r) Dewclaws in the dog and many other 

 mammals reveal an original five-toed condition, (d) The 

 whale is a very specialized mammal, and therefore full of 

 useless remnants. Whales have no hair, but rudiments of 

 hair in the skin show that their ancestors were hairy. 

 They have no hind limbs, but rudiments are found buried 

 in the flesh, and therefore useless. The baleen whales 

 have no teeth, but rudiments of teeth are found buried 

 in the jawbone, and are never cut. (if) We have already 

 said (page 249) that snakes have lost their limbs by disuse. 

 This is true, for rudiments of limbs are found buried in the 

 flesh of some (the python), and, of course, useless. (/) 

 Even in man, although he is far less specialized than most 

 mammals, rudiments are found. Among these may be 

 mentioned the muscles for moving the ears and for mov- 

 ing the scalp. Rudiments must be regarded as demon- 

 strative proof of the derivative origin of organic forms. 



Whole Skeleton. — We have taken only the limbs 

 as best illustrating the principle, but the same is true of 

 the whole skeleton. The skeleton, as a whole, is in all 

 vertebrates the same machine, but modified in all its parts 

 to adapt it for various purposes — viz., as a swimming 

 machine, a walking and running machine, or a flying ma- 

 chine, and all without essential change of plan. 



Other Systems. — The whole argument for deriva- 

 tive origin of organic forms is based on the equal bal- 

 ance of the two ideas — essential identity and adaptive 

 modification. If the modification be too great, the essen- 



