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 s P I1- al 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, I rom the upper extremity, where the inner and 
the outer sacs are in contact, there projects a long cilium, 
oi fine pointed bristle, which is not retractile, and appears 
to be immoveable. 
llie weapon of ofi'ence 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 
. 6 bottom of the interior of the sac there is a body, in 
ape resembling a saucer, in the centre of which stands 
SrUa ^ ova b s °bT body, hearing on its summit a cal- 
tat 6 ° US i* s extremity, and bifid, or sagit- 
0 * ®’ at lts base - This dart can he projected at the will 
the 6 ai ^ ma ^ an ^ a o a 'U withdrawn into the sac. When 
witlffo ° ns ^ e mstinct is exerted, the darts are thrust out 
while at° C ' euteiaD 8 the tissues of the prey, retain it : 
potent Same thne, in all probability, a subtle but 
„1 P° 1Son is injected, the effects of which we have 
already alluded to. 
this is a modern discovery. The circumstance in 
