118 



THE HARMONIES OF NATURE. 



that comes within its reach, for, seized by its irresistible arms, 

 it is soon conveyed to the gaping mouth, ever ready to ingulf 

 it in a living tomb. Yet it is not by brute force alone that the 

 rapacious polyp thus overpowers its prey, but by means of those 

 remarkable * thread, or urticating cells ' which have been given 

 to many others of the humbler submarine animals, but chiefly to 

 the polyps and acalephas, and, like the stings of the nettle or 

 the poison-fangs of the viper, not only wound but paralyse 

 resistance by a venomous secretion. 



These urticating organs, which are disseminated in multitudes 

 over the tips of the tentacles, are composed of a delicate mem- 

 branous sac (a), enclosing a 

 much thicker one (b), which 

 is open at one extremity, the 

 aperture being stopped by the 

 end of a more or less irregular 

 short stiff sheath (c) some- 

 times giving attachment to 

 several distinct rays or spines 

 (cT) applied together, which is 

 fixed to the edges of the aper- 

 ture, and occupies the axis of 

 the inner sac. To the ex- 

 tremity of this sheath a long 

 frequently toothed filament (e) 

 is attached, and lies coiled up 

 round the central sheath, and 

 in close contact with the walls 



of the sac. The latter are very elastic, and seem to be tensely 

 stretched by the conta'ned fluid during life, for on pressure the 

 sac suddenly bursts, and its contents are evacuated so rapidly as 

 hardly to allow of the process being traced. The violent protu- 

 sion of the serrated filament, accompanied by an acrid secretion, 

 causes many a worm or crustacean of equal or superior strength, 

 that might have gone forth as victor from the struggle for life, 

 to succumb to the insidious Actinia, and is even in many cases 

 exceedingly irritating to the human skin. Besides enabling 

 its possessor to derive his subsistence from animals whose 

 activity, as compared with his own, might be supposed to have 

 removed them altogether out of the reach of danger, these stings 



