HALF AN HOUR WITH SEA- ANEMONES. 121 



tentacles alternating with each other. That end of 

 the animal on which these organs are placed, is called 

 the " disk," and that by which the entire animal 

 attaches itself to rocks and stones, the "base." 

 This base seems to be very sensitive to injury, 

 although the other parts of the animal are tolerably 

 hardy, and capable of soon recovering any damage, 

 or even of forming two individuals out of one when 

 torn or lacerated. The base has, in some species, 

 the power of moving, or crawling, much like a snail, 

 but more slowly. That part of the animal termi- 

 nated at one end by the disk, and at the other by 

 the base, is usually called the " column." This is of 

 various lengths, in some species being very short 

 indeed, and in others, as in the plumose anemone 

 (Actinoloba dianthus, Fig. 62), very long, with 

 a broad, flat base. The power of expansion and 

 contraction which we noticed as peculiar to the 

 jelly-fishes, and the means by which they progressed 

 through the water, is possessed in a modified form 

 by the column of the sea-anemones. Its use, as we 

 shall see, is, however, quite different to that to 

 which it is put in its allies. Each tentacle is hollow, 

 and communicates with the body-cavity. By the 

 muscular contraction of the column, the fluid in the 

 body chambers is forced into the tentacles. The 

 latter are thus elongated, whilst the reverse process, 

 of course, withdraws them. Some species, as the 

 Opelet, cannot withdraw the tentacles ; but others, 

 as the smooth anemone, do so until the creature 



