THE CCELENTERATA 31 



of its relatives that live in southern seas, and those that 

 lived in the seas which in ages gone covered these lands, 

 and which have left their skeletons well preserved in our 

 limestone hills. The name of this one is Caryophylla. 



What we learned of the structure of cells in the last 

 chapter will help us to understand what follows. 



The anemones, like everything else that lives, are made 

 up of cells, as have been described, but in this group i.e. 

 the Ccelenterates there occur cells of a peculiar kind, 

 called Nematocysts, which are very complicated bits of 

 mechanism. 



Coiled within each of these Nematocysts is a fine thread 

 (Gr. nema : a thread ; cyst : a cell), which, fine as it is, 

 is hollow, and may be said to be a part of the outer layer of 

 the cell greatly prolonged and invaginated to the interior, 

 like the finger of a glove would be if drawn inward from its 

 tip until it was inside the palm ; only in the cell the finger 

 would be many times longer than the receptacle, and it 

 would have to be coiled to lie within it. 



At the base of the thread are several very sharp barbs 

 very sharp they must be, since the entire machine is smaller 

 than a full stop on this page. A little " trigger " acts like 

 the hook on a child's " jack-in-the-box," and keeps thread 

 and barbs packed within (see Fig. 7 in Plate 13). 



Now this is what happens. When any little fish, worm, 

 or other wanderer in the sea approaches one of these 

 ccelenterates, or rather comes in contact with one, a number 

 of the little triggers are touched, the sting cell suddenly 

 contracts, and shoots out the barbed portion, which pene- 

 trates and sticks into the skin of the visitor. The thread, 

 which is so fine that no awl is required for its insertion, 

 follows suit, and at the same time an irritant fluid is injected 

 into the visitor's flesh, causing, to a small animal, paralysis 

 or death, and to a large one considerable local discomfort. 

 A bather who has collided with a jelly-fish preferably 



