70 



LIFE BY THE SEASHORE. 



of the shore crab is changed by the digestive process from 

 greenish to red a change which it is easy to imitate in the 

 laboratory by immersing a fresh shell in dilute acid. Also, 

 the hard shell has been rendered brittle and is easily 

 pulverised. From these observations we might deduce the 

 conclusion which has, indeed, been reached by experiment 

 that the anemone secretes an acid digestive fluid. 



Next in order of abundance on the East Coast comes the 

 cave-dwelling anemone (Sagartia troglodytes}, a form which 



in spite of its 

 abundance is much 

 more difficult to 

 find than either 

 of those already 

 mentioned. If you 

 are idly gazing into 

 a shallow rock pool 

 floored with varie- 

 gated sand or fine 

 gravel, you may 

 sometimesfindthat 

 as you gaze certain 



FIG. 25. The cave-dwelling anemone, Sagartia troglodytes, star-like patches 

 Note the beautifully marked tentacles, and especially differentiate them- 



selves from the 



background by a regularity of shape, not to be ascribed to 

 current action. If you touch these spots in order to 

 investigate the matter, the star disappears, leaving an ill- 

 defined hollow. Study this phenomenon still more closely 

 by scraping the sand away with your fingers, and you will 

 find a small sea-anemone, attached to the rock surface which 

 floors the pool, and protruding its crown of tentacles through 

 the sand. The attachment is relatively slight, and the 

 anemone can be readily removed and placed in a clean pool 

 or a collecting jar. It is very contractile, and by the time 

 the process is completed will probably be reduced to the 

 condition of a brownish button, partially invested in its 

 own white stinging-threads (acontia), which are shot out in 

 abundance as soon as it is touched. It rapidly recovers, 

 however, and will probably soon unfold its tentacles, and 

 display the variegated marking which gives them so deceptive 



