198 



ZOOLOGY. 



354. Natural Affinities and Analogies of Structure. 

 -This tendency of nature to observe one general plan in the 



Fig. 152. The Human Vertebra the Type of all Skeletons. The 

 references are explained below, Fig. 153.* 



construction of her works leads to another sort of relation- 

 ship, which naturalists have called natural affinities. These 

 affinities are always the stronger 

 that they bear on organs of se- 

 condary physiological importance, 

 and necessitate less change in the 

 general plan of the organization. 

 Thus it is obvious that the lion, 

 cat, and tiger have strong natural 

 affinities; between the lion and 

 the dog there still exist natural 

 affinities, though obviously less 

 marked ; but between the lion 

 and the shark they are extremely 

 feeble, excepting in so far as they 

 both belong to the vertebrata ; 

 finally, between a fish and an 

 oyster there are none, inasmuch 

 as these two beings are formed on 

 plans essentially distinct. 



355. Between natural affi- 

 nity and analogy there is this 

 essential distinction, affinities are 



lis 



Fig. 153. The Ideal Vertebra, 

 as viewed by Oken, Spix, and 

 St. Hilaire as the Type of ail 

 Osseous Structures. f 



* From the Eaces of Men, by E. Knox, 



t [Copied from Owen. c, centrum ; ns, neural spine; ks, haemal spine; 

 d, diapophyses ; pi, pleurapophyses ; n, neurapophyses ; h t haemapophyses ; 

 p, parapophyses ; z, zygapophyses.] 



