82 ANIMAL LIFE 



fish plants its suckered feet firmly on the ground, and 

 then applies two or more ranks of these suckers against 

 the valves (fig. 16), straining to separate them. The 

 oyster claps its shell together at the first touch, but 

 after the tireless starfish has maintained an even 

 strain for a time, the oyster from fatigue and want of 

 oxygen opens its valves. Through the opening the 

 starfish inserts its acid stomach, and the secretion of 

 this falling on the oyster's muscle weakens it. The 

 valves gape open, and the starfish at its leisure absorbs 

 the contents. 



Away from the shore great activity is employed. 

 The maintenance of equilibrium, the pursuit of food, 

 and the avoidance of powerful agitation imply sus- 

 tained movement. Jelly-fish, cuttlefish, fish of all 

 kinds, are in constant muscular tension. Hunger 

 follows ; the cold open sea and strong aerated water 

 sharpen the appetite that constant exercise produces. 

 Around these hungry swimmers is a drifting stream 

 of wriggling, darting, whirling particles — the offspring 

 of the shore. These enter into every mouthful of 

 water that a fish takes to discharge over its gills, 

 or that a jelly-fish inhales for a fresh spurt, and the 

 choice of food is soon determined. 



Fish rarely masticate their food. Their jaws, 

 preoccupied with breathing, can only momentarily 

 hold and bolt it ; and since plants above all other 

 aliments need grinding, they form the least desirable 

 choice. Hence it is that the oily rowing-shrimp 

 becomes the mackerel's bonne bouche and the favourite 



