30 COBALS AND CORAL ISLANDS. 



The Actinia appears, at first thought, to be well prepared 

 for securing its prey through its numerous tentacles. But 

 these are generally too short for prehension. Yet the disk often 

 aids them by rolling over the captured animal, and pushing it 

 down into the stomach. At the same time, the mouth and 

 stomach are both very extensile, so that an Actinia may swal- 

 low an animal nearly as large as itself; it gradually stretches 

 the margins of the mouth over the mollusk or crab, until the 

 whole is enclosed and passed into the digestive sac ; and when 

 digestion is complete, the shell and any other refuse matters 

 are easily got rid of by reversing the process. 



But the Actinia owes nearly all its power of attack to its 

 concealed weapons, which are carried by myriads. These 

 are what Agassiz has called lasso-cells, because the little cell- 

 shaped sheath contains a very long slender tubular thread 

 coiled up, which can be darted out instantly when needed. 

 As first observed by Agassiz, the tubular lasso escapes from 

 the cell by turning itself inside out, the extremity showing it- 

 self last, and this is usually done " with lightning-like rapidi- 

 ty." Then follows the poison. The lasso-cells (called often 

 nettling cells, and by Gosse cnidoe, and thread capsules) are 

 usually less than a two-hundredth of an inch in length ; but 

 they are thickly crowded in the larger part of the skin or walls 

 of the tentacles, and about the mouth ; also in the walls of the 

 stomach, and within the visceral cavity in white cords hanging 

 in folds from the edge of the septa. Thus the polyp is armed 

 inside and out. The mollusk or crab that has the ill luck to 

 fall, or be thrown by the waves, on the surface of the pretty 

 flower is at once pierced and poisoned by the minute lassos, 

 and is rendered incapable of resistance. 



The following figures, by Dr. Karl Mobius. of Hamburg, il- 

 lustrate admirably these organs. The views are magnified 



