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 natm-alists sea mosses. 



606. Of the order of Polypes called Helianthoida I 

 have already noticed quite particularly one group, the 

 Actiniae (§ 576), as illustrating well the characteristics 

 of the Radiata. There need to be added here .to whr.t 

 has been said some farther statements in regard fo 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 Actiniae 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- 

 cies 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- 



