94 



ANNELIDA. 



birds, or the brilliant decorations of insects: green, 

 yellow and orange, blue, piu-ple and scarlet, — all the 

 hues of the rainbow j)lay U23on them with the changing 

 light, and shine with a metallic effulgence only com- 

 parable to that which adorns the breast of the humming- 

 bird. But it is not only for their dazzling beauty that 

 these worms are remarkable ; many of them are armed 

 with spines, that constitute important w^eapons of defence ; 

 each of these sjDines is seen, under the miscroscope, to be 

 a perfect harpoon, its jDoint being j^rovided with a double 

 series of strong barbs, so that when the creature erects its 

 bristles, much more formidable than the spines of a 

 hedgehog, the most determined enemy would scarcely 

 venture to attack it. These spines are all retractile, and 

 can be dra^vn into the body by the muscular tube from 



Fig. 64.— sea-house. 



which they spring. It would be superfluous to point out 

 the danger that would accrue to the animal itself by the 

 presence of such instruments embedded in its body, as by 

 every movement they would be forced into its own flesL. 

 The contrivance to obviate such an accident is as beauti- 

 ful as it is simple : every barbed sj^ine is furnished with a 

 smooth, horny sheath, composed of two blades, between 

 which it is lodged (Fig. 64), and these, closing upon the 

 barbs, when they are drawn inwards, effectually protect the 

 neighbouring soft parts fi-om laceration. 



