468 RADIATA: POLYPI. 



pairs is some multiple of six six pairs in the first series ; 

 six in the second ; twelve in the third ; twenty-four in 

 the fourth ; forty-eight in the fifth, etc. And the com- 

 partment between the two septa of each pair opens into 

 the hollow tentacle above. 



Professor Verrill has shown that the tentacular compartments indi- 

 cate the ambulacral segments of the Polyp. 



The food of polyps consists of small marine animals, 

 which are secured by means of the tentacles, and the 

 curious and wonderful organs called lassos. 



On the tentacles, and about the mouth, and on the walls of the 

 stomach, and in the white cords often seen hanging from the folds of 

 the radiating septa, are vast numbers of cnidse or lasso-cells, each one 

 being less than - 2 io of an inch in length. In each cell there is a long, 

 slender coiled-up thread or lasso ; and these threads can be darted 

 forth with almost lightning-like rapidity, and the little animal upon 

 which they strike, and into whose tissues they penetrate and carry 

 poison, as is believed, is instantly paralyzed, and is thus readily secured 

 by the hungry polyp for food. The lasso in some cases is twenty to 

 forty times as long as the cell. 



After digesting the soft parts of the animals which they 

 capture, they eject the shell or other hard parts through 

 the mouth. And it may be stated here that the substance 

 of some kinds of polyps, as the Actiniae or Sea-anemones, 

 is so extensible that they can swallow and eject shells of 

 almost as great diameter as themselves. The expansion 

 and contraction is accomplished by means of two sets of 

 muscles, one set circular, and another longitudinal. 



After being digested the food passes into the main cavity 

 of the body, and thence into the chambers and tentacles, 

 thus nourishing every part. 



The Polyps have no proper nervous system. The sense 

 of touch is distributed throughout the whole animal ; but 

 as to sight, it is quite remarkable that some kinds of Sea- 



