496 ACTINIA OR SEA-ANEMONE. 



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 secre- 

 tion is formed, become smaller, or disappear^ 



1062. The essential difference between the Hydra and the 

 Actinia consists in this ; that in the former the stomach occu- 

 pies the whole volume of the body, the membrane which lines it 

 being the same with that which serves as the general envelope ; 

 whilst, in the latter, the stomach has walls of its own, being 

 suspended (as it were) in tiie middle of the body, and leaving a 

 considerable space between its exterior surface and the general 

 envelope. This cavity is divided by vertical partitions, which 



FIG. 617. A, SEA-ANEMONK seen from above. B, SECTION OF SEA-ANEMONE ; a cavity 

 of stomach, b surrounding chambers. 



pass in a radiating direction from one membrane to the other, so 

 as to form a considerable number of chambers arranged round 

 the central digestive sac. In these chambers the germs of young 

 Actiniae are evolved. There is not any regular communication 

 between the chambers and the stomach ; although it would seem 

 that an opening must be occasionally formed, as young polypes 

 are often sent forth by the mouth ( 1067). The partitions all have 

 openings, however, by which the chambers communicate with 

 each other ; and there is also a free entrance from them into the 

 tubes of the hollow tentacula, which are formed of a membrane 

 like the envelope of the body, and are provided with an orifice 

 at their extremity, which the animal has the power of closing. 



