the Succession of Organized Beings. 161 



no distinction between the different relations which existed among 

 animals. Affinity and analogy, so dissimilar in their essential cha- 

 racters, were constantly mistaken one for the other; and upon the 

 peculiarities which struck the observer most at first sight, animals 

 were brought together, sometimes upon the ground of true affinity, 

 sometimes, also, upon the ground of close analogy ; and though 

 comparative anatomy did put the mistakes arising from such confu- 

 sion right, by showing that external appearances were sometimes 

 deceptive, and that a more intimate knowledge of internal structure 

 was necessary fully to understand the real relations between animals, 

 there remained, nevertheless, a degree of uncertainty in may jcases, 

 as long as the principles of affinities and of analogies were. not fully 

 distinguished. Every naturalist now knows that true relationship — 

 affinity — depends upon a unity in structuie, however diversified the 

 forms may be under which their fundamental structure is displayed. 

 For instance, the affinity of whales and the other mammalia was not 

 understood before it was shown that, under the form of fishes, these 

 animals had truly the same structure as the highest vertebrata. 



Again, the forms of cetacea exemplify the analogy there is be- 

 tween whales and fishes. They are related to mammalia ; they are 

 analayous to fishes ; they bear close affinity to the mammals which 

 nurse their young with milk ; they have rather close analogy to the 

 gill-breathing fishes. 



Since the fossil animals which have existed during former periods 

 upon the surface of our globe, and which have successively peopled 

 the ocean and the dry land, have been more carefully studied than 

 they were at the beginning of these investigations ; since they are 

 no longer considered as mere curiosities, but as the earlier represen- 

 tatives of an order of things which has been gradually and succes- 

 sively developed throughout the history of our globe, facts have been 

 bi'ought to light which now require a very careful examination, and 

 will lead to a more complete understanding of the various relations 

 which exist between these extinct-types and those which still continue 

 to live in our days. Upon close comparison of these facts, I have 

 been led to distinguish two sorts of relations between the extinct 

 animals, and those of our days, which seem to me to have been 

 either overlooked or not sufficiently distinguished. Indeed, the 

 general results derived from Palceontological investigations, seem 

 scarcely to have gone beyond showing that the animals of former ages 

 are specifically and frequently also generically distinct from those 

 of the present creation ; and also to establish certain graduation be- 

 tween them, agreeing more or less with the degree of perfection 

 which we recognise between the living animals according to their 

 structure. 



It is now pretty generally understood that fishes, which rank lowest 

 among the Vertebratay have existed alone during the oldest periods ; 

 that the reptiles which, in the gradation of structure, rank next 



VOL. XLIX. NO. XCVIl. — JULY 1850. L 



