ACTINIA OR SEA-ANEMONE. 483 



Actinias confine themselves to the smooth sands, on the surface 

 of which they spread out their tentacula, and beneath which they 

 withdraw when danger threatens. Although the body has, in 

 general, no further covering than the leathery envelope already 

 mentioned, there are a few species which, by means of a glutin- 

 ous exudation from the body, form a kind of case by attaching 

 together bits of shell, grains of sand, and other small substances. 

 This casing would seem to have for its purpose the concealment 

 of the animal, as much as its direct protection. Individuals of 

 the same species, inhabiting deep water, as if aware that they do 

 not require such a mode of concealment, form no extraneous 

 covering, but leave the surface clean ; and this then acquires 

 more vivid and varied tints, whilst the glandular warts by which 

 the glutinous secretion is formed, become smaller, or disappear. 

 One curious worm-like form (the Edwardsid), which seems to 

 unite the Actiniae with the Holothurise ( 1112), constructs a 

 membranous tube for its habitation, and strengthens this with 

 fragments of shells and gravel. It lives buried in the sand, as 

 does also another remarkable allied form described by Mr. Gosse 

 under the name of Peachia, which differs from all other Polypes 

 in its possession of a posterior orifice. 



1125. The stomach in the Actinia is furnished with walls of 

 its own, and suspended (as it were) in the middle of the body, 



FIG. 712. A, SEA-ANEMONE seen from above. B, SECTION OP SEA-ANEMONE ; a, cavity 

 of stomach ; b, surrounding chambers. 



leaving a considerable space between its exterior surface and the 

 general envelope. This cavity is divided by vertical partitions, 

 which pass in a radiating direction from one membrane to the 



