HIS ZOOLOGICAL RELATIONS. 41 



undoubtedly are, but these are merely diiferences in 

 degree — modifications of parts common to the whole 

 rather than the creation or introduction of what is 

 new and essentially original. Comparing the various 

 orders and families of the vertebrate class, the lower 

 with the higher, and the higher with those next above 

 them, it seems that adaptive modifications, rather than 

 independent and repeated creations, have been the 

 governing method in structural advancement. As a 

 skUful engineer models the primal idea of the steam- 

 engine so as to adapt it for stationary, locomotive, or 

 marine purposes, and this without inventing a new 

 machine, so the original conception of the vertebrate 

 skeleton is merely modified to suit it for the respec- 

 tive requirements of the fish, the reptile, the bird, 

 and the mammal. And so in like manner it happens 

 with the ordinal and generic differences that take 

 place within the respective classes : they are modifica- 



essential as to preclude a comparison between them, or as teing 

 other than a difference in degree, I cannot shut my eyes to the 

 significance of that all-pervading similitude of structure — every 

 tooth, every bone, strictly homologous^ — ^which makes the determina- 

 tion of the difference between homo (man) and pitliecus (monkey) 

 the anatomists' difficulty." — (Professor Owen " On the Characters, 

 etc., of the Class Mammalia," in the Journal of the Idnncean Society 

 for 1867.) And to the same effect the great Swedish naturalist 

 admitted, now more than a century ago — " Nullum characterem ad- 

 huc eruere potui, unde homo a simia intemoscatur." — (Linnaeus, 

 Fauna Suecica.) 



