General physiology; an outline of the science of life . e, which are unicellular fresh-waterRhizopocla whose naked protoplasmic bodies are fixed in a verydelicate urn-shaped or flask-shaped capsule, take up the materialfor their tiny dwellings with their finger-like pseudopodia out ofthe mud of the pools and lakes at the bottom of which they structural material of their shells is very varied, but in many 1 Of. Verworn (88). ELEMENTARY VITAL PHENOMENA 149 cases the shells are composed of one definite material (Fig. 49).Thus, forms occur that employ only cases of the silicious At gee o
General physiology; an outline of the science of life . e, which are unicellular fresh-waterRhizopocla whose naked protoplasmic bodies are fixed in a verydelicate urn-shaped or flask-shaped capsule, take up the materialfor their tiny dwellings with their finger-like pseudopodia out ofthe mud of the pools and lakes at the bottom of which they structural material of their shells is very varied, but in many 1 Of. Verworn (88). ELEMENTARY VITAL PHENOMENA 149 cases the shells are composed of one definite material (Fig. 49).Thus, forms occur that employ only cases of the silicious At gee ordiatoms, while others employ only sand-grains of certain sizes, and stillothers particles of mud. It has been thought that the Difflugia;select their material from substances at their command. But itcan be proved, at least in some cases, that no real selection existshere in the same sense as in food-ingestion by the above-men-tioned cells. The fact that forms from one and the same localityemploy only a certain material depends rather upon the circum-. Fig. 49.—Various Difflugia-sheUs, constructed of : A, diatom-cases ; B, fine sand-grains ; C, fine andcoarse sand-grains ; D, diatom cases and sand-grains ; E, coarse sand-grains ; F, the same formas E, but made of splinters of blue glass. stance that in the given locality only this one material is at , , the dwelling-place of the form that constructs its shell outof mud or substance excreted from its body be examined, it isfound that here other materials, perhaps diatom-cases or sand-grains, are wholly wanting. If, however, such forms be given thepossibility of getting other material, by the introduction of veryfinely pulverised sand or, still better, very finely ground, colouredglass into the culture-vessel in which they live, it is found that theindividuals arising by reproduction surround themselves with adelicate shell of sand or splinters of coloured The circum-1 Of. Verworn (90, 1). 150 GENERAL PHYSIOL
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Keywords: ., bookcentury1800, bookdecade1890, bookidgen, booksubjectphysiology
