88 LIFE IN THE SEA [CH. 



a great extent that of the development of organs for 

 the capture of food. Such organs are the jaws, teeth 

 and some other structures in fishes ; the suctorial 

 mouths and rasping tongues of lampreys ; the suckers 

 and horny beaks of the squids and cuttle-fishes, the 

 pincers, maxillae and mandibles of the Crustacea ; 

 the blood-sucking mouths of leeches and some other 

 worms ; the scraping tongues, or radulae, of whelks ; 

 the tentacles and stinging cells of sea-anemones and 

 jelly-fish ; the suckers and protrusible stomachs of 

 starfish and sea-urchins, etc. These are examples 

 which illustrate the great diversity of methods by 

 which the predatory marine animals capture their 

 prey. The majority of nektic and benthic animals 

 hunt for the organisms which serve them as food, 

 even the microscopic amoebae and infusorians appear 

 to roam about incessantly in search of food. Many 

 marine animals are cannibalistic, and not a few of 

 them are quite promiscuous in their choice of food, 

 but as a rule each species eats by preference one or 

 a few species of food organisms. A small minority 

 of the nektic animals, chiefly the whalebone whales, 

 and some pelagic fishes like the herring and mackerel, 

 are plankton feeders. The whales take in mouthfuls 

 of water, and then on closing the jaws this water is 

 forced out through a sieve formed by the frayed-out 

 margins of the whalebone plates. The herring and 

 mackerel take water into the mouth and then the 



