The Sea-Anemone. 



17 



attached to them. In very transparent anemones it can 

 be seen that the tentacles project over the spaces between 

 the partitions. The stomach is not simply a cavity hol- 

 lowed out in the body, as in the hydra, but is another hol- 

 low bag hanging down inside the outer one. 



When very yonng the sea-anemone is 

 like the hydra, but as it grows, the 

 upper end of the body-tnbe folds inward 

 till it hangs down inside as an open sac, 

 abont half as long as the body. To illna- 

 irate this, take a glove-finger and ont 

 off the end to represent a hydra, then 

 turn in the end for some distance, and 

 the part banging down inside will repre- 

 sent the stomach of the anemone. The 

 proboscis of the hydra and the stomach 

 of the sea-anemone are therefore precisely similar in their origin, 

 though different in their use ; that is, they are homologous. While 

 digestion is going on, the lower end of the stomach is closed by 

 muscles, and refuse matter is afterward ejected through the mouth. 



The tentacles are covered with lasso-cells, or thread- 

 cells, similar to those of the hydra. The white threads 

 thown out from tiny loop-holes in its sides when an anem- 

 one is disturbed, also bear myriads of these little weapons. 



Sea-anemones are often produced from buds, which 

 form around the base of the old ones. If one is torn in 

 scraping it from the rocks, the portion left behind will 

 become a perfect animal. 



Fig. 5. 



