200 ON THE ANIMAL KINGDOM. 



order Alga and the Infusoria is the supposed presence in 

 the latter of a nervous system and an absorbent intestinal 

 canal, neither of which however as yet has been ob- 

 served, nor indeed reckoned to exist in the lowest animals 

 except from analogical induction. We are therefore forced 

 to acknowledge that like the letter V plants and animals 

 present two distinct branches united at their base. Now, 

 as the great object of the present Essay is to trace one of 

 the ramifications of this dichotomous tree to its extreme- 

 fibres, I shall proceed to ascertain, if possible, the first na- 

 tural groups into which the animal kingdom may be re- 

 solved ; and for this purpose shall follow the excellent me- 

 thod devised by M. Virey. 



In the first place, we observe a tribe of beings which 

 have one principal centre to their nervous system, the 

 great trunk of which, with the said centre, is contained 

 in a bony articulated case, which forms the axis of the 

 whole body, and composes the vertebra? and scull of these 

 animals, which are therefore named V.ERTEBRATA. 



In a second form of animals the skeleton is as it were 

 external, so as to envelop the whole body, and is divided 

 by transverse folds into a certain number of rings, to the 

 internal surface of which the muscles are always fixed. 

 Their nervous system consists of two long strings of medul- 

 lary matter, passing through the whole of the body, and 

 united to each other at small distances into several knots, 

 or ganglions. These ganglions may be said to perform 

 for the parts which surround them the function of so many 

 brains, and for a certain period even to be sufficient for 

 nervous sensibility after the animal has been cut in pieces. 

 The animals constructed on this plan have obtained the 

 name of Annulosa. 



In a third form there is no articulated skeleton either 



