DISTRIBUTION OF ORGANISMS. 



171 



scarcely be said that the radiate sub-kingdom comes before the 

 articulate, though the one is lower in organization than the 

 other. There is indeed reason to believe that the great classes 



O 



of the Articulata are distinct stirpes, the commencement of 

 each of which is little more than a step from the inorganic 

 form of matter. This may seem inconsistent with the maxim, 

 Natwa per saltum nihil agit ; but maxims must be obedient 

 to facts, not facts to maxims, and we may deem that a leap 

 which in reality is none. 



That the Annelides (worms) are the humblest of the com- 

 monly recognised articulate animals, there is now no doubt ; 

 for the character of red blood, which was attributed to them by 

 Cuvier, and held as a mark of great though anomalous eleva- 

 tion, has been explained satisfactorily as a mistake, being 

 merely a hue possessed by the fluid element of the blood, and 

 not due to red corpuscles, as in the vertebrata. Four leading 

 forms in this class are described. Of the TuUcolidce, or those 

 inhabiting tubes, the Serpula is an example. It forms for its 



FIG. 86. 



FIG. 87. 



Group of Serpulce, with 

 the branchial tufts of 

 one of them expanded. 



Nereis. 



