30 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 Coelenterata includes the Polypes and 
Medusz, and in the closest connection with it stands 
the interesting class of the Spongiade, especially in- 
structive as affording direct evidence of the doctrine of 
Descent. The organs of these animals are nearly always 
