1 70 ECHINODERMA TA. PART m. 



The backs of all the star-fishes are covered with 

 most minute movable spines, and with microscopic 

 organs like minute pincers, called pedicellarise, which 

 are diffused generally over the surface, and form dense 

 groups round the spines. They have a slender, con- 

 tractile, calcareous stem, and a head formed of two 

 blades, which they continually open and shut, the whole 

 being coated with a soft external tissue. They grasp 

 anything very firmly, and are supposed to be used to 

 free the star-fish from parasites. In some species of 

 Goniaster the pedicellarise resemble the vane of an 

 arrow, and are so numerous as to give a villous appear- 

 ance to the skin of the back. 



On the under-side of each ray of a star-fish, a cen- 

 tral groove or furrow extends throughout its whole 

 length, and the semi-calcareous flexible membrane which 

 covers the back and rays not only bends down round 

 the sides of the rays, but borders both edges of the 

 grooves. Upon these edges ridges of small calcareous 

 plates beset with spines are placed transversely : they 

 are larger near the mouth, and gradually decrease in 

 size as they approach the point of the ray. 



Interior to the spines, these ridges are pierced by 

 alternate rows of minute holes for the long rows of feet, 

 which diminish in size to the end of the ray. The feet 

 are contractile muscular tubes communicating through 

 the holes with internal muscular sacs, which are re- 

 garded as their bases. The sacs are full of a liquid, 

 and when the animal compresses them the liquid is 

 forced through the holes into the tubular feet, and 

 stretches them out ; and when the muscular walls of the 

 hollow feet are contracted, the liquid is forced back 

 again into the sacs, and the feet are drawn in. The 

 liquid is furnished by a circle of small vascular tentacles, 

 or sacs, surrounding the mouth, which are both loco- 



