70 EXPLANATIONS. 



vague degree, alike. The progress of the linefi 

 becomes clearest when we advance into the verte-^ 

 brate sub-kingdom. We can there trace several] 

 of them with tolerable distinctness, as they singly] 

 pass through the four classes of Fishes, Rep- 

 tiles, Birds, and Mammals ; the Birds, however, 

 being a branch in some part derived equally 

 with the reptiles from fishes, and thus leaving 

 some of the mammal order in immediate con- 

 nexion with the reptiles. The lines or stirpes 

 have all of them peculiar characters which persist 

 throughout the various grades of being passed 

 through, one presenting carnivorous, another 

 gentle and innocent animals, and so on. We 

 have, therefore, in the animal kingdom, not one 

 long range of affinities, but a number of short 

 series, in each of which a certain general character 

 is observable, though not always to the exclusion 

 of the organic peculiarities of families in neigh- 

 bouring lines, especially in the class of reptiles. 



According to this view, the matrix of organic 

 life is, speaking generally, the sea. Fluid, re- 

 quired for all embryotic conditions, is also neces- 

 sary to the origination of the various stirpes of 

 both kingdoms. The whole of the lowest animal 

 sub-kingdom (Radiata) is aquatic ; so are nearly 



