20 THE DOCTRINE OF DESCENT. 



own rank and station among its own immediate 

 kindred. 



Some insight into this classification of the animal 

 kingdom is naturally indispensable to any one, who 

 wishes to test and understand its reasons, and to render 

 an account of it is an essential part of our task. 



Since Cuvier's reconstruction of Zoology in the early 

 part of this century, our science has been familiarized 

 with the expression " type," or " fundamental form," 

 introduced, long before, by Buffon. Cuvier, by ex- 

 tensive dissections and comparisons, first proved that 

 animals were not, as people were formerly inclined to 

 suppose, made on a last or shaped upon a block ; but 

 that they fall into several great divisions, in each of 

 which expression is given to a peculiar constitution, 

 arrangement, and distribution of the organs ; in short, 

 to a peculiar style. The sum of these characteristic 

 peculiarities, as well as the whole of the species united 

 in it, was termed a " type." Various views, it is true, 

 even now prevail as to the extent of several of these types 

 or families, as we will already term them ; but if we dis- 

 regard the dubious, and in many ways suspicious, exis- 

 tences, generally comprised under the name of primordial 

 animals, there is a general agreement as to the following 

 number, but less as to the sequence of the animal types, 

 than as to those groups, each of which has its peculiar 

 physiognomy and special characteristic structure. 



The class Ccelenterata includes the Polypes and 

 Medusae, and in the closest connection with it stands 

 the interesting class of the Spongiadae, especially in- 

 structive as affording direct evidence of the doctrine of 

 Descent. The organs of these animals are nearly always 



