Starfishes. 



FIG. 30. 



the name. They all possess a central disc from which 

 five to twenty arms radiate. The surface is generally 

 roughened with stiff ridges and spiny points, and 

 under this layer 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 ; 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 

 chiefly are found on sea- 

 weeds. The other and 

 commoner kinds 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- 



'-IIIQ little sninpQ whnsf 



ous nuie spines wnose 



extremities are movable, 



and two- or three- 



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



gans, which assist in seizing the prey, the name 



2 



larva or P lutens of the Brittle-star 



(pphioiepis). 



mouth; s, stomach; s, calcareous 

 skeleton. 



