is cut down the middle of the head and the gash re- 

 newed for several days so that the wound is not re- 

 paired, there will after a time be two complete heads 

 on the single body. 



The familiar white fresh-water planarian of the 

 northeastern United States is Procotyla fliiviatilis, 

 which has a blunt head; also an adhesive organ, in 

 the center of the front edge, which is used to capture 

 prey. Procotyla belongs to the dendrocoelids, most 

 of them white planarians, which are much more 

 abundantly represented in the fresh waters of Europe 

 and Asia. 



The marine triclads are found mostly on gravelly 

 or rocky shores in temperate or cold seas, and are 

 known especially from the Mediterranean and Black 

 Seas, though they occur also on other protected 

 shores of the North Atlantic and of Japan. None is 

 yet described from the Pacific coasts of the Ameri- 

 cas or from Africa. A well-known marine triclad of 

 the American Atlantic coast is BdeUoiira Candida, 

 shaped something like a spearhead. It clings to the 

 leg bases and gills of the horseshoe crab, feeding on 

 small organisms brought in by the movements of the 

 host. On English shores the commonest triclad is 

 Procerodes iilvae, a tiny gray-banded or streaked 

 worm with two eyes on the blunt head, and a broad 

 rear end. It abounds under stones in places where 

 fresh water trickles down a cliflf or beach and is 

 known for its ability to endure great changes in the 

 salinity of water. 



The land planarians have thoroughly exploited the 

 use of slime as a means of overcoming the hazards 

 of terrestrial life. Their invasion of the land is limited 

 mostly to damp forest floors, where they hide during 

 the heat of day under stones, fallen logs, or leaf mold, 

 coming out only at night to find their prey. They 

 seize, mount upon, and subdue small animals, often 

 even snails or earthworms. Occasionally they turn up 

 in well-watered gardens, where they hide in the day- 

 time under boards or pots. Land triclads are often 

 more brightly colored than their fresh-water relatives. 

 When not uniformly gray, green, brown, or black, 

 they may have black stripes on a yellow or orange 

 ground, or light stripes on a dark ground. A few are 

 blue or violet. Though there are hundreds of tropical 

 and subtropical species, some of these a foot or two 

 long, only a few species live in moist temperate woods 

 or in temperate gardens. Those seen most often in 

 the United States are not native planarians, but tropi- 

 cal ones shipped in with ornamental plants. Trans- 

 planted tropical planarians survive briefly in green- 

 houses or gardens, but usually die out, even in the 

 kindest temperate climates, because they do not be- 

 come sexually mature. The most successful tropical 

 transplant, perhaps originally from the Indo-Ma- 

 layan region, is Bipaliiun kewense, named for Kew 

 Gardens near London, where it was first discovered. 



Since it reproduces readily by asexual fragmentation, 

 it has become permanently established in gardens in 

 California, Louisiana, Florida, the West Indies, and 

 other subtropical places. Large size (up to 14 inches 

 long), striped pattern, and an expanded half-moon- 

 shaped head edged with numerous minute eyes, 

 make it easy to recognize. 



THE POLY CL ADS 



The polyclads grace marine shores in every part 

 of the world, most of them gliding about on the ocean 

 bottom to seek their prey, or hiding under stones and 

 in damp rocky grottoes when the tide is out. Some 

 tolerate brackishness, but only one species, living in 

 Borneo, is known from fresh water. Though they are 

 named for the multiple branchings of the digestive 

 cavity, most polyclads are instantly recognizable by 

 their broadly oval, extremely flattened, leaflike bod- 

 ies. Few follow the elongate fashion of triclads. On 

 the whole these are turbellarians of fairly large size. 



A planarian flatworm, Snrncelis amcricnim, from a 

 Missouri cave. This white dendrocoelid flatworm, 

 with two rows of eyes, has many close relatives in 

 Eurasia. { Ralph Buchsliaum ) 



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