Starfishes. 



FIG. 



the name. They all possess a central disk from which 

 five to twenty arms radiate. The surface is generally 

 roughened with stiff ridges and spiny points (paxillcz), 

 and under this integument is a layer of calcareous plates ; 

 each arm has on its under surface a groove in which 

 lie the ambulacral vessels, and the nerve-cord, which 

 is tubular; and many starfishes have imperfect red 

 eyes at the end of this ambulacral groove. 



On our sea-shores there are two kinds of star- 

 fishes to be found; the first kind or Brittle-stars have 

 a rounded, or five-sided flat disk at the centre, and 

 slender, jointed, snake-like arms, which, as they do 

 not contain processes of the viscera, the animal can 

 break off when irrita-- 

 ted. These brittle-stars 

 are chiefly found on sea- 

 weeds. The other and 

 commoner kind of star- 

 fishes have thick, flat- 

 tened triangular arms 

 which are continuous 

 with, and not jointed to, 

 the disk. These have 

 a mouth in the middle 

 of the under surface of 

 the body, and around 

 it on the skin are curi- 

 ous little spines whose T ^jS^J). pluteus of the Bn ' ttte - star 



extremities are movable, ', mouth; *, stomach; .9, calcareous 

 skeleton. 



and two- or three- 



bladed, like little pincers. To these little grasping or- 

 gans, which assist in seizing the prey, the name 



E 2 



