252 THE CANADIAN NATURALIST. [Aug. 



tliis general style of construction does not apply, and wliicli have, 

 in the words of Agassiz, a 'Vertical axis around which the pri- 

 mary elements of their structure are symmetricidly arranged," 

 conforming in this respect, and also often in other points, to the 

 symmetry of the plant, rather than to that of the more perfect ani- 

 mals. We would thus obtain what is perhaps the most obvious of 

 all primary divisions of animals, — that into those with bilateral 

 symmetry and those that are radiated, or the Artiozoaria and the 

 Actinozoaria of Blainville. We shall soon find, however, on more 

 detailed examination, that this division is very unequal, since the 

 first group includes by far the greater part of the animal kingdom, 

 and its members are nearly as dissimilar among themselves as any 

 of them are from the radiates. 



Penetrating a little deeper into structural character, we find 

 that one large group of the bilateral animals possesses an internal 

 skeleton, arranged in such a way as to divide the body into an 

 upper chamber holding the brain and nervous system, and an 

 under chamber for holding the ordinary viscera; whereas in the 

 greater number of the bilateral animals and all the radiates, there 

 is but one chamber for containing the whole of the oroans. The 



O O 



first of these groups, from the vertebrae or joints of the backbone, 

 peculiar to its members, we name Vey^tehrata, and all the other 

 animals Invertebrata, as proposed by Lamarck : this division cor- 

 responds to the enaima and anaima of Aristotle. Here also how- 

 ever we have a very unequal division, — the invertebrata being a 

 vast and heterogeneous assemblage. 



If, however, after separating the vertebrata on the one hand, 

 and the radiata on the other, we study the remainder of the ani- 

 mal kingdom, we find that it readily resolves itself into two groups, 

 known as the Articulata and the Mollusca. We thus reach the four- 

 fold division of Cuvier; which is by much the most natural and 

 philosophical yet proposed, however much it may be carped at by 

 some merely anatomical systematists. This system may be sum- 

 marised as follows : 



Provinces or Branches of the Animal Kingdom. 



1. Yertebrata, including Mammals, Birds, Eeptiles, and 

 Fishes, All these animals are bilateral and symmetrical, have an 

 internal vertebrated skeleton, a brain and a dorsal nerve-cord lodged 

 in a special cavity of the skeleton. With reference to the general 



