98 



The Insides and the WorXings of Living Things 



ning throughout the series, notwithstanding the wide range 

 of Hving conditions to which the various forms are adapted. 

 The wing of the bird, we saw, is built on the same pattern 

 as the leg of the elephant and the flipper of the whale, or 

 the wing of the bat. The limbs of mammals are built on the 

 same pattern as the limbs of reptiles and amphibians as well 

 as of birds. Now we may go further and find that the 

 Greenland whale has, in addition to the flipper with an arm- 

 like framework, a set of bones corresponding to the hind leg, 

 which never appear at the surface (Fig. 27) . 



^f^T^r-'yyy'-'t'"''.^^ 



■^rf^0^^9y%:i.:-;y 





Fig. 27. Hind Leg of the 

 Greenland Whale 



No explanation has been oflfered for the pres- 

 ence of these bones except the assumption that 

 the whale is a decendant of a form which in 

 some past era had all four legs, and that along 

 with the changes in mode of living the hind legs 

 became reduced — and, in some species, com- 

 pletely lost. After Eschricht and Reinhardt. 



The relationship of snakes to lizards, alligators and 

 turtles has been deduced from the many resemblances in 

 structural details and in development, notwithstanding the 

 absence of legs in snakes and their uniform presence in the 

 other " reptiles." Yet the python retains a vestige inherited 

 from a hypothetical ancestor with paired legs, in the form 

 of two horny hooks connected with a short chain of reduced 

 bones that correspond to the hip girdle in other reptiles. 

 Many similar relics are found in the early stages of develop- 

 ment (Fig. 28) . 



We need not look through rare museum specimens for 

 evidences of kinship among animals of different orders or 

 classes. Every modern animal is a living museum of such 



