86 SECRETS OF EARTH AND SEA 



far the biggest animals of which we have any knowledge 

 are the various kinds of whales still flourishing in the sea. 

 A mechanical limit is set to the size of land-walking 

 animals, and that limit has been reached by the elephant. 

 " Flesh and blood," and we may add " bone," cannot carry 

 on dry land a greater bulk than his. He is always in 

 danger of sinking by his own weight into soft earth and 

 bog. His legs have to be much thicker in proportion 

 than those of smaller animals made of the same material 

 or they would bend and snap. His feet have to be 

 padded with huge discs of fat and fibre to ease the local 

 pressure, and his legs are kept straight not bent at the 

 joints, when he stands (a fact to which Shakespeare makes 

 Ulysses refer), so that the vast weight of his body shall 

 be supported by the stiff column formed by the upper 

 and lower half of the limb-bones kept upright in one 

 straight line. A well-grown elephant weighs five tons. 

 Compare his weight and shape with that of a big whale- 

 bone whale ! No extinct animal known approaches the 

 existing whale in bulk and weight. He is 80 to 90 ft. 

 long, and has no neck nor any length of tail. His out- 

 line is egg-like, narrower at the hinder end. He weighs 

 200 tons forty times as much as a big elephant and 

 is perfectly supported without any strain on his structure 

 by the water in which he floats. There is no such limit 

 to his possible size as there is in the case of land-walk- 

 ing animals. * But it seems probable that he too is 

 limited. in size by mechanical conditions of another kind. 

 Probably he cannot exceed some 90 ft. in length and 200 

 tons of bulk on account of the relatively great increase 

 of proportionate size and power in the heart required in 

 order to propel the blood through such a vast mass of 

 living tissue and keep him "going" as a warm-blooded 

 mammal. The original pattern the small dog-like 

 ancestor of the whale cannot be indefinitely expanded 



