STRUCTURE OF RADIATA.—ECHINODERMATA. 1 25 
117. The circular arrangement of the organs of Radiated 
animals is a striking point of resemblance to the Vegetable 
kingdom ; and it has frequently caused mistakes to be made 
in regard to the Sea-Anemones and other large polypes, 
which, when their mouths are open and their arms spread 
out, look so much like the blossoms of some of the Com- 
posite tribe of plants, as to have received the name of animal 
But there is yet a stronger analogy between the 
lower members of the Radiated group and the Vegetable 
kingdom ; for among the former, as in the latter, we find 
@ union of many individuals, which are capable of existing 
separately, into one compound structure, having a plant-like 
form. This is the nature of the stem of Coral (fig. 76) ; 
which is, in fact, the skeleton of one of these compound 
systems, consisting of a number of polypes united by a jelly- 
like flesh ; just as the woody stem of a tree is the skeleton 
that supports a vast number of buds, each of which is capable 
of living by itself This aggregation results from the in- 
definite multiplication of parts by the process of gemmation 
or budding, and from the persistence of the connexion 
between these parts, notwithstanding that, if separated, 
they can maintain an independent existence. To the tree- 
like fabrics thus produced, the name Zoophytes (animal 
plants) is commonly given; and ordinary observers often 
find it difficult to get rid of the idea of their vegetable 
rigin. The animals that formed them are, of course, fixed 
to one spot during all but the earliest periods of life; and 
the amount of movement which they perform, for the pur- 
pose of obtaining and securing their food, is very little 
greater than that which is witnessed in the Sensitive plant 
and Venus’s fly-trap. 
118. The class of Ecurvopermarta receives its name from 
the prickly character of its covering, which is evident enough 
_ in the Echinus or Sea- Urchin, and in the Star-fish; but there 
_ are other animals, sufficiently resembling these in general 
_ structure to be united in the same class, which have a body 
_ entirely soft,—namely, the Holothurie (fig. 67), commonly 
termed Sea-Cucumbers. This class ranks as the highest 
_ among the Radiata, in regard to general complexity of struc- 
_ ture. The skeleton of the Sea-Urchin, Star-fish, and other 
_ amimals resembling them, is a box-like shell or “test,” formed 
