1 6 OUTLINES OF NATURAL HISTORY. 



iug itself and changing its place if necessary. At tlie end 

 of the animal opposite to the fixed base is placed the 

 mouth, in the centre of a rounded, smooth space, which 

 is surrounded by a fringe of numerous holloAv processes 

 or "tentacles." 



Both the body and tentacles are formed out of two 

 membranes, an outer and an inner (shown by the dark 

 and light lines in fig. 5, B) ; and the outer layer of the 

 skin contains a vast number of microscopic stinging 

 organs or " nettle-cells," essentially similar to those which 

 we have already seen in the Fresh -water Polype. The 

 skin, also, is very contractile, and the animal can pull 

 itself together into a mass when irritated, or even when 

 left uncovered by the retreating tide. 



The tentacles are hollow, and communicate with the 

 cavity of the body. They can be drawn in at will, and 

 are the organs by which the animal captures its prey. 

 At their bases is seen a circle of from eight to twenty- 

 five bright blue spots, which are perhaps rudimentary eyes. 



The internal anatomy of the Sea-anemone is of a very 

 simple character. The mouth opens into a globular 

 stomach (fig. 5, B, b), and this opens below by a wide 

 aperture into the general cavity or space included within 

 the walls of the body. This last-mentioned space is filled 

 with sea-water, mixed with the products of digestion, and 

 it is subdivided by a number of upright membranous 

 plates, which wall off the body -cavity into a series of 

 chambers or compartments. 



The digested portions of the food pass through the 

 stomach into the general cavity of the body, and the 

 indigestible portions are got rid of through the mouth. 

 There is no nervous system, nor are there any breathing- 

 organs, nor any organs of the circulation. 



The Actinia mesemhryanthemtim is strictly marine, and 

 is found abundantly on the coasts of Britain between 

 tide-marks, adliering to stones, or expanding its beautiful 

 flower-like disc in shallow rock-pools. It varies extremely 

 in colour, being usually of a liver-brown or olive-green 

 colour, but not uncommonly being purplish-red, or grass- 



