and the Elements in which they live. 381 
joints may be, they never combine in such a manner as to divide 
the body into distinct ridges, in which the form is always elonga- 
ted and vermiform, never provided with articulated rings, however 
humerous and diversified the locomotive appendages may be, and 
in which the foremost joints hardly ever assume a peculiar struc- 
ture with the appearance of a head. This class for which the 
name of Worms is best retained, will contain the Helminths and 
Annelides exclusive however of the vermiform parasitic Crusta- 
cea, which embryology has taught us to refer unhesitatingly, to 
the class of Crustacea. The extraordinary diversity which exists 
among these animals renders it rather difficult to subdivide them 
into natural groups, and to assign to these groups a natural suc- 
cession agreeing with the gradation of their structure, as there 
are so many the development of which is as yet very imperfectly 
known, and others which undergo so complicated metamorphoses 
as to leave great doubt respecting their natural relations to each 
other. However, there can be no doubt that Helminths rank 
lower than Annelides, for their structure indicates plainly their 
inferiority, and their mode of existence within other animals 
Shows that they do not even reach that degree of independence 
which might allow them a free existence. 
to which we refer also the Cirripeda notwithstanding their trans- 
formations, also the Lernean parasites, though they may assume 
