66 ANIMAL LIFE 



minute plants enclosed in flinty cases, surpass sand- 

 tfniins in multitude; they encrust the shore, fill the 

 beds of rivers, and, borne on the air, are showered 

 down upon sea and land from the tropics to the 

 poles. 



The oldest and simplest way of catching food is 

 that practised by the lower aquatic animals : sponges, 

 corals, animalcules, and all encrusting organisms. It 

 consists in drinking the water and sifting from it the 

 minute organisms that abound therein. It is carried 

 out by the aid of those minute, vibratile hairs or 

 cilia which, originally used for drawing the animal 

 through the water, now draw water through the 

 animal. Into the vortex created by the beating of 

 these organs will be haled from the surrounding 

 catchment-area all those particles which cannot 

 resist suction, however gentle ; and as animal and 

 plant spores abound in fresh and salt water during 

 the spring and summer, the particles inhaled will 

 consist partially, at least, of minute organisms, and 

 upon these the sponge or coral is able to live. In a 

 similar manner, barnacles throw out and draw in their 

 casting-nets and collect the fine wreckage of the coast 

 which constitutes their food. 



Most of the animals that feed in this way are 

 fixed, and when at the approach of winter the supply 

 of minute organisms falls off, they have no means of 

 leaving the coast or lake shore for more teeming 

 water. In order that they shall not starve during 

 this season, most encrusting animals lay up during 



