CHAPTER XV 



COMPARATIVE LOCOMOTION 



Summary.— Comparative locomotion among terrestrial mammals: the 

 man, the horse, the elephant — Comparative locomotion among 

 different kinds of birds — Classification of different types of loco- 

 motion — Comparative locomotion of tortoises and lizards ; frogs, 

 toads, and tadpoles ; snakes, eels, and fish ; insects and spiders. 



Comparative Locomotion. — The most interesting 

 feature of zoology is not so much the descriptive and 

 systematic account of the various forms met with in the 

 animal kingdom as the tracing of association between 

 form and function. As comparative anatomy and 

 physiology become more and more allied, doubtless 

 more fundamental morphological laws will be dis- 

 covered, and these perhaps will enable us to predict 

 the function of any particular organ from an ana- 

 tomical inspection. 



We are certainly very far from being in a position 

 to understand this association in the case of most 

 organs ; but the mechanical action of some of them 

 is already so familiar that the physiological function 

 can be explained on anatomical grounds. The form 

 of the vertebrate skeleton, the volume and length of 

 the muscles, and the relative dimensions of the long 

 bones are necessarily closely associated with the kind 

 of locomotion habitual to the animal. Inviolable 

 mechanical laws govern this association, some of them 



