24 INTRODUCTION TO ZOOLOGY. 



If the tentacula be destroyed, others are soon after formed. 

 If the animal be cut across into two distinct portions, the 

 upper part continues to take food as usual, though for a 

 time unable to retain it. If severed longitudinally, each 

 half becomes perfect, so that two Actinias are produced; 

 nay, if it be so destroyed that not a fragment is left except 

 a portion of the base, a fresh offspring is soon raised up 

 to fill the place of the parent. 



The following characteristic occurrence is related by 

 Dr. Johnston: — "I had once brought to me a specimen of 

 Actinia genimacea, that might have been originally two 

 inches in diameter, and that had somehow contrived to 

 swallow a valve of Pecten maximus* of the size of an 

 ordinary saucer. The shell fixed within the stomach was 

 so placed as to divide it completely into two halves, so that 

 the body, stretched tensely over, had become thin and 

 flattened like a pancake. All communication between the 

 inferior portion of the stomach and the mouth was of 

 course prevented; yet, instead of emaciating and dying of 

 atrophy, the animal had availed itself of what had un- 

 doubtedly been a very untoward accident to increase its 

 enjoyments and its chances of double fare. A new mouth, 



furnished with two rows of nume- 

 rous tentacula, was opened up on 

 what had been the base, and led to 

 the under-stomach. The indivi- 

 dual had, indeed, become a sort of 

 Siamese twin, but with greater in- 

 timacy and extent in its unions!" 



Belonging to the same order, but 

 to a different family from the Sea- 

 anemones {Actiniiclce), are the 

 Coral-building Polypes of tropical 

 seas {3IadrepliyUicea), some of 

 TiR. i3.~CABvopnTtLiA. ^^^^ich have been taken in deep 



water off theBntish coast (Fjy. 13). 

 Their structures have been the wonder of the navigator and 

 the theme of the poet; and while Science endeavours to 

 reveal the process by which they are upreared, she but 

 adduces another example that, under the flispensations of 

 Providence, the mightiest of works can be executed by 

 the weakest of agents. 



The great extent of some of the coral reefs is very rc- 

 * The commoa Scallopt 



