RADIATES. 349 
analogy to the Hydra during the temporary connection 
of the young Hydras with it, their stomachs having a 
communication with the stomach of the parent. These 
beautiful and delicate animals were formerly supposed to 
be vegetable, and were called by naturalists sea mosses. 
606. Of the order of Polypes called Helianthoida I 
have already noticed quite particularly one group, the 
Actiniz (§ 576), as illustrating well the characteristics 
of the Radiata. There need to be added here to what 
has been said some farther statements in regard to their 
structure and habits. It is the beauty of the expanded 
disks of these and other allied animals that gives the name 
Helianthoida to this order, this word being derived from 
two Greek words meaning sun and form. In the trop- 
ics they are peculiarly brilliant, and many travelers speak 
most enthusiastically of the gorgeous spectacles which 
groups of them often present. 
607. Some Actiniz live on smooth sands, spreading 
out their tentacles for prey, and retiring beneath the sand 
when danger threatens. But most of them attach them- 
selves to rocks, often adhering so firmly that they can 
not be detached without lacerating them. And when 
portions of the disk are left fixed to the rock, new ani- 
mals will be formed from them, just as is the case with 
sections of Hydras (§ 604). There is one species that 
fastens itself to some shell; and it is observed that the 
Hermit Crabs are fond of taking up their abode in such 
shells, making a singular sort of partnership. 
608. The muscular structure in some of the larger spe- 
cles is very distinct, and exhibits great power in action. 
They can not only master small shellfish and Crustacea, 
but even Crabs, Prawns, and other Crustacea of consid- 
erable bulk. The mouth is capable of wide distention, 
so that animals can be taken in which one should suppose 
to be inadmissible. It is amusing to witness the strug- 
gles of some animal that has, in walking about, come over 
one of these gaping mouths, as it is caught by the tenta- 
