POLYPES, 



53 



According to Corda, each tentacle forms a slender mem- 

 branaceous tube, filled with an albuminous substance 

 nearly fluid, mingled with some oily particles. This 

 substance, at certain definite points, swells out into 

 tubercles or dense warts, which run round the tentacle in 

 a spiral line. Each wart is furnished with several spine- 

 bearing vesicles, which are organs of touch, and with an 

 organ of highly curious structure, which is the weapon of 

 offence. 



The organ of touch consists of a fine sac, enclosing 

 another with thicker walls, within which there is a small 

 cavity. From the upper extremity, where the inner and 

 the outer sacs are in contact, there projects a long cilium, 

 or fine pointed bristle, which is not retractile, and appears 

 to be immoveable. 



The weapon of offence is placed in the midst of these 

 spines, in the centre of each wart. It consists of an oval 

 transparent sac, imbedded in the substance of the wart, 

 with its perforated extremity exactly at the surface. At 

 the bottom of the interior of the sac there is a body, in 

 shape resembling a saucer, in the centre of which stands 

 a small oval, solid body, bearing on its summit a cal- 

 careous dart, pointed at its extremity, and bifid, or sagit- 

 tate, at its base. This dart can be projected at the will 

 of the animal, and again withdrawn into the sac. "When 

 the prehensile instinct is exerted, the darts are thrust out 

 with force, and, entering the tissues of the prey, retain it : 

 while at the same time, in all probability, a subtle but 

 potent poison is injected, the effects of which we have 

 already alluded to. 



But this is a modern discovery. The circumstance in 



