702 



COELENTERATA-II. CNIDARIA. 



up into a tentacle. These fleshy "septa" are infoldings of the inner layer 

 of the wall of the sac-like body. They do not all arise at the same time, 

 nor do they all project equally far into the body cavity. Only some of them 

 run out far enough to connect the two tubes in the upper part of the body. 



This dividing up of the body into compartments is one of the chief dis- 

 tinctions between the Sea-anemone polyp and the Hydra polyp. In many 

 other respects the Sea-anemone closely resembles the Hydra. It has the 

 same power of retracting its tentacles and reducing its whole body to a bud- 

 like shape. It captures food with its tentacles, and digests it within its 

 body cavity, throwing out at the mouth all that it cannot assimilate. It has 

 also a limited power of motion, not, however, like the Hydra, using its 

 tentacles for this purpose, but gliding along on its base. 



The Anemone is still richer than the Hydra in stinging cells. It has been 

 calculated that some Anemones possess as many as 43,000,000 of stinging 

 cells in one tentacle, and in the whole body something like 6,450,000,000. 

 The stinging cells in Anemones measure from 3!^ to ^oVo ^ an i ncn ^ ne 

 thread being often twenty times as long as the cell, and more richly supplied 

 with barbs than are those of the Hydra. These cells, too, in the Anemone, 

 are not merely found in the outer skin, but form in great quantities in the 

 gastric cavity. 



The outer skin of the Anemone is not always smooth and jelly-like ; it is 

 often covered with wart-like protuberances, which sometimes secrete a sticky 

 fluid. Some Anemones have, further, a circle of " eyes " placed like a 

 necklace round the body. Each of these has a lens and simple optic nerve, 

 but the latter is not connected with any other nerves. From time to time, 

 as the Anemone grows, it is able to cast off its outer skin, after having 

 formed a new one beneath it ; the old skin can often be seen in a wrinkled, 

 dead-looking condition encircling the base of the animal. 



Although none of the Sea-anemones found on our own shores attain the 

 size of some of the tropical specimens, they are very beautiful and well 

 worthy of study. A few only can here be briefly described. 



The Plumose Anemone (Fig. 10) and the Daisy Anemone are two of the 

 English varieties of the Sagartiadse, so-called after a tribe in the army of 



Xerxes, known for their practice of en- 

 tangling their enemies by means of noosed 

 ropes. All these Anemones possess, attached 

 to the septa of the gastric cavity, tangled 

 masses of stinging threads resembling 

 tangles of white cotton. These they can at 



Fig. 10. THE PLUMOSK ANKMONB 

 (Actinoloba dianthus). 



Fig. 11. EDWARDBIA. 



will shoot out of the mouth, and, in some cases, through apertures at the 

 sides of the body, for the purpose of paralysing their enemies. In large 



