APPENDIX 



covering because their blood is cold and changes with the 

 temperature of the medium in which they live. 



Besides giving warmth to a land mammal, hair acts as a 

 protection for its tender skin; but since a whale lives in the 

 water, where bruises or abrasions are unlikely, such pro- 

 tection is unnecessary. With the loss of hair the sweat and 

 oil glands which are present in the skins of land mammals 

 finally disappeared. 



When any creature becomes aquatic it must necessarily 

 develop means for progression through the water, and thus 

 the caudal portion of the whale's body by degrees expanded 

 into the wide, flat, boneless tail, or flukes. But instead of 

 being vertical to the axis of the body like the tail of a fish, 

 the whale's flukes are horizontal, obviously to give the animal 

 greater facility in rising to the surface to breathe. 



With the development of the flukes there came a change 

 in the whale's fore-limbs, which were flattened and covered 

 with connective tissue and blubber. The excellent paddles 

 thus formed, while probably of little use in forward motion, 

 assist in rapid turning and act as balancing organs to keep 

 the animal upright in the water. In some species an adipose 

 dorsal fin has also developed as a further balancing aid. 



During the development of the flippers and flukes the 

 hind-limbs, which were no longer of use to the whale, be- 

 came small and weak, sunk into the blubber and finally dis- 

 appeared altogether, the greatly modified pelvic elements and 

 nodules of bone or cartilage representing the femur alone 

 remaining. 



The heads of most cetaceans are long and pointed, acting 

 as a "cut-water," but one of the most remarkable aquatic 

 adaptations is the position of the nostrils, or blow-holes, 

 which open upon the very summit of the head, in either a 

 single or double aperture, instead of at the end of the snout. 

 The cause of this migration of the nostrils is obvious, for in 

 this position the blowholes first appear at the surface and 

 the whale can begin to breathe while the rest of its body 

 is yet under water. 



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