ORGANISM OF THE STAR-FISH. 135 



from their hole, and to grope backwards and forwards through the 

 water, evidently seeking the nearest ground to lay hold of. Those 

 that reach it first, immediately affix their suckers, and, by con- 

 tracting, draw a portion of their body after them, so as to enable 

 others to attach themselves, until, pulley being added to 

 pulley, their united power is sufficient to restore the star-fish to 

 its natural position. 



This act of volition is surely remarkable enough in an animal 

 which hardly possesses the rudiments of a nervous system, but 

 the simple mechanism by which the suckers are put into motion 

 is still more wonderful. Each of these little organs is tubular, 

 and connected with a globular vesicle filled with an -aqueous 

 fluid, and contained within the body of the star-fish, immedi- 

 ately beneath the hole from which the sucker issues. When 

 the animal wishes to protrude its feet, each vesicle forcibly con- 

 tracts, and propelling the fluid into the corresponding sucker, 

 causes its extension ; and when it desires to withdraw" them, a 

 contraction of the suckers draws back the fluid into the expand- 

 ing vesicles. All these little bladder-like cavities are connected 



Section of a ray of Asterias Rubens, 



Showing the arrangement of the calcareous pieces, a oblong calcareous plates united in the 

 median line, b smaller lateral plates. 



with vessels, which communicate with a vascular circle surround- 

 ing the mouth ; while the internal walls, both of the suckers 

 and the system of communicating vessels, are furnished with 

 vibratory cilia, through whose agency a continual circulation of 

 the fluid they contain goes on within them, and serves to aerate 

 the blood. 



Not only the suckers, but also the rays from which they pro- 

 ceed, are extremely flexible in every direction, for the skeleton 

 of a star-fish, or that part which remains when all the soft flesh 

 has been removed, is a wonderfully beautiful structure, consist- 



