ELEMENTARY VITAL PHENOMENA 



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cells. But from this common nutrient liquid each kind of cell 

 removes the substances necessary for its life ; the mucous cell 

 takes substances different from those taken by the ganglion-cell, 

 the muscle-cell substances different from those taken by the car- 

 tilage-cell, the liver-cell substances different from those taken by 

 the sense-cell, and so on. The different cells choose entirely 

 different materials, each one according to its need. 



This phenomenon of food-selection is, perhaps, more remarkable 

 in certain free-living cells that take in solid food. Cienkowski 



FIG. 47. Four individuals of Coleps hirtus swarming about and ingesting a ball of food. 



('65), who has studied in detail the life of the lowest Rhizopoda, 

 the naked monads, gives an interesting description of how Colpo- 

 della and Vampyrella, two simple, naked rhizopod-cells, procure 

 their food, which consists of living alga-cells. Cienkowski relates 

 as follows : " Although the zoospore- and amoeba-conditions of the 

 monads are only naked protoplasmic bodies, their behaviour in 

 seeking and ingesting food is so remarkable that it seems to be 

 the work of conscious beings. Thus, Colpodella pugnax pierces 

 the Chlamydomonas, sucks up the chlorophyll that flows out, and 



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