254 THE CANADIAN NATURALIST. [A 



us:. 



account, themselves constitute a new style ; and tlie Provinces 

 3IoUuscolda and Annuloida of Huxley, which, as their names 

 indeed import, are in the main merely simple forms of Mollusca 

 and Articulata. 



6. Division or Provinces into Classes. 



Having formed our Primary divisions or Provinces on the 

 ground of type or plan, we must, in dividing these into classes, 

 have regard either to subordinate details of plan, or to some other 

 ground. In point of fact, naturalists seem to have tacitly 

 agreed to form classes, on what Agassiz terms the " manner in 

 which the plan of their respective great types is executed, and 

 the means employed in their execution." In other words, they 

 have in forming classes adopted, perhaps unconsciously, a func- 

 tional system, similar to that employed by Oken in forming his 

 primary groups. They have taken the relative development of 

 the four great functional systems of the animal, — the sensative, the 

 locomotive, the digestive, and the reproductive. This is very 

 manifest in the ordinary and certainly very natural sub-division of 

 the vertebrates into the four classes of Mammals, Birds, Reptiles,^ 

 and Fishes. The Mammals are the nerve or sensuous animals, 

 representing the highest development of sensation and intelligence. 

 The Birds are eminently the locomotive class. The Reptiles 

 represent merely the alimentary or vegetative life. The Fishes are 

 the eminently reproductive or embryonic class. 



If this is a natural division of vertebrates into classes, and if 

 the other three Provinces are of equivalent value, then there 

 should be but four classes in each, one corresponding to each of 

 the great functional systems. We may name the first of these 

 the nervous class ; the second, the motive class ; the third the 

 nutritive class ; the fourth, the reproductive or embryonic class. 

 Let us then endeavour, as a test of the truth of this system, to 

 make such an arrangement of the classes of the animal kingdom. 



* The oiinphibia, as Dana well argues on the principle of cephalisation, 

 are clearly Reptiles, because we arrange animals in their mature and 

 not in their embryonic condition, and because the points of reproduction 

 in which Amphibia differ from ordinary reptiles, have relation to an 

 aquatic habitat, and are ordinal or rank characters merely. 



