LIFE ON THE EARTH. 29 



the series of affinities, and illustrated modern types 

 by ancient parallels. 



The adherence of plants and animals to the several 

 leading types is sufficient in most cases to leave no 

 doubt of the place of each; the typical peculiarity 

 influences all parts of their structure, the leaves, 

 flowers and fruit of a plant the limbs, dermal cover- 

 ing, composition, colour and temperature of the blood 

 in an animal. So that a single leaf will generally 

 decide the place of a plant in the three great divi- 

 sions a single drop of circulating fluid, the eye, a 

 bone, a shell or crust, that of an animal. As an 

 exception among plants we may mention those of 

 the family Smilacese which yield Sarsaparilla, whose 

 leaves are veined with the net-work of Dicotyledones, 

 but whose seeds are formed on the model of Monoco- 

 tyledones. Among animals the Polyzoa or Bryozoa 

 were long ranked as Radiate animals, and there is 

 now a difference of opinion regarding the place of 

 the conspicuous family of Echinodermata, which 

 some place at the head of the Radiata, but others 

 join with Annulose animals. 



Each great type comprehends several considerable 

 subdivisions, in each of which a reigning idea may 

 often be traced in the structure, and exemplified in 

 the function. These are again subdivided in a man- 

 ner suggestive of other ideas. For example, Mam- 



