METHODS OF ATTACK AND DEFENCE 105 



Weapons. — Under this heading we shall consider the 

 various structures which have for their object the disable- 

 ment of foes, but only so far as they are distinct from 

 structures, such as jaws, teeth, etc., which are concerned 

 with feeding in the strict sense, i.e. with the preparation 

 of food for the work of digestion. 



Weapons acting partly mechanically, partly by means of 

 Poison. — Frequently, the mechanical action of a weapon is 

 designed merely to inflict a small wound into which a supply 

 of poison may then be poured, and also in a certain measure 

 to hold the animal while it is being paralysed. The 

 commonest weapons of this type are the nematocysts of 

 Ccelentera, the structure of which is familiar to every 

 zoological student. Briefly stated, a nematocyst is an oval 

 bag filled with fluid and produced at one end into a long 

 whip-like process usually provided with barbs. In the 

 unexploded state the long process is tucked into the cavity 

 of the dilated portion in a neat spiral. The nematocyst is 

 contained in a special pear-shaped cell, or cnidoblast, from 

 the free margin of which there projects a short sensory 

 process or cnidocil. When this process is stimulated the cell 

 contracts and the fluid within being incompressible the 

 thread is jerked out of the capsule with great force. The 

 free end of the nematocyst, while lying in the " ready " 

 position, is bathed in a poisonous fluid. Some of this 

 adheres to the lash when ejected, and enters the wound, or 

 according to another view, makes its way down the interior 

 of the lash and escapes by a tiny aperture at its end 

 (Cuenot). 



The arrangement of the nematocysts varies according to 

 the species, but they invariably occur in masses or 

 " batteries." These are particularly numerous on the 

 tentacles, and, in anemones, upon the mesenteries, in which 

 position they serve to administer the " coup de grace " to 

 any organism which still gives signs of activity. Further, 

 in many anemones the mesenteric filaments bear long 

 thread-like processes termed " acontia," which are also 

 armed with numerous nematocysts, and can be protruded 



