FIELD BOOK OF PONDS AND STREAMS 



ature is quite as important as food in determining where 

 they live. A single species often lives in springs or ponds 

 which are very different in other ways, shallow or deep, rapid 

 flowing or slow, so long as their waters are uniformly cold. 

 The European Planaria alpina occurs in the high cold lakes 

 of the Alps, while in lower regions it is not found at all in 

 similar lakes where the water is warm, but only in rapid 

 brooks and in springs whose temperature is more like that of 

 the mountain lakes. Dr. Kathleen Carpenter has suggested 

 that some planarians are relicts of the Ice-Age, animals 

 brought from the north by the great ice-sheet, and left 

 stranded in warmer regions where they are now making the 

 best of it, living only in the coldest places. 



Food. — All planarians are carnivorous and often cannibal- 

 istic. They thrive on crushed snail-meat and beef-liver, 

 devouring it greedily at night, the time when they are most 

 active. If a hungry Planaria macidata (Fig. 98) is turned 

 on its back in a drop of v.'ater and a piece of *snail-meat held 

 within its reach it will thrust out its pharynx and suck up the 

 meat juice till it is full to bursting. Planarians will gather in 

 groups ten to fifty strong upon pieces of meat which are 

 dropped into their dishes. They will eat hard-boiled yolk of 

 egg. The milky planarian, Dendroccflum lacteum (Fig. 97), 

 will fill its food canal with it till its whole back is yellow. 



A few minute turbellarians, the rhabdocceles (Fig. 96), are 

 vegetarians, living on algae, diatoms, and especially Spirogyra, 

 on which they are sometimes abundant. 



Aquarium study. — Planarians are easy to collect and can be 

 kept in aquaria for long intervals with very little trouble. 

 They cling to leaves when they are pulled from the water 

 or to stones and can be easily lifted from them with the point 

 of a knife. The aquarium for them should be supplied with a 

 shallow bed of clean sand, a few pebbles, several sprays of 

 Myriophyllum or some other water plant, and clean water kept 

 cool and out of bright light. Planarians cannot stand heat or 



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