CATALOGUE 
OF 
BRITISH ECHINODERMA. 
INTRODUCTORY REMARKS. 
The Position of Echinoderms in the Animal Kingdom.—The 
Ecuryoperma belong to that division of the Animal Kingdom in 
which the organism consists of more than one cell, and is always, 
at some period or other of its life-cycle, derived from a single 
egg-cell which has been fertilized by a sperm-cell. In other words, 
it is one of the Metazoa. In the course of development from the 
egg there appears, in addition to the gastric cavity, another space 
which is known as the body-cavity or ccelom. 
Among the Metazoa Celomata the Echinoderma occupy a very 
isolated position, for we know of no link which unites them to 
any other “ phylum” or great division of this series. 
The Symmetry of Echinoderms.—It would appear that, at a very 
early stage in the evolution of the Echinoderma, the adult tended 
to acquire a marked radial symmetry ; but, at first, the number 
of rays was by no means constantly five ; now the symmetry is so 
generally quinqueradial that wonder is nearly always expressed 
when the number five is diminished or increased. 
The first point, then, which we have to notice is the possession 
of rays; the “rays” and the “body” generally may appear to be 
conterminous, as in the Holothurian or the Echinus, or the “ body ” 
may seem to gradually pass into the “rays,” as in the common 
Starfish, or may be quite distinct from it, as in the Brittle-star and 
Sand-star. Where a marked distinction can be made between the 
body and the rays, the former is often called the disk and the 
latter the arms. 
The radial symmetry which is indicated externally by the rays 
is to be observed in some at any rate of the internal systems of 
organs. It is characteristic of Echinoderms to have a special system 
of tubes, not represented in other types of animal life, some of the 
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