ELEMENTARY VITAL PHENOMENA 



235 



intestinal epithelium-cells (Fig. 45) ; and, finally, various 

 kinds of plant-cells (Fig. 24, a, and Fig. 35). The movement of 

 Amceba can serve as a type (Fig. 95). This organism is the lowest 

 of all living things, and its formless body holds within itself the 

 whole secret of life. Taken with a pipette in a drop of water 

 from the bottom of a pond and brought under the microscope 

 upon a slide, the amoeba-cell appears as a small grey semi- 

 transparent droplet of a more or less pronounced spherical form ; 

 in the central portion lie the nucleus and usually a contractile 

 vacuole, surrounded by a more or less granular endoplasm, while 

 the peripheral layer consists of a more hyaline exoplasm. If 

 this drop of living substance be observed for some time, it is 



Fig. 95. — Aiiu'^ha in eight successive stages of movement. 



seen that at some point of its surface the spherical mass bulges 

 out in the form of a lobate projection ; this becomes constantly 

 larger and extends itself farther and farther, more protoplasm 

 flowing into it constantly ; the phenomenon spreads from the 

 peripheral parts toward the centre, so that a continual streaming 

 takes place from the centre toward the periphery in this so-called 

 pseudopodium (Fig. 95). Frequently the whole protoplasmic 

 mass of the amoeba flows over into this one lobate projection, so 

 that the body forms a single extended mass, as can be observed 

 especially in Amceba Umax. Frequently, however, the centrifugal 

 protoplasmic streaming of the pseudopodium becomes interrupted, 

 while at the same time at another point of the surface a second 

 pseudopodium is formed in the same manner by a centrifugal 



