SECT, i STRUCTURE AND PHYSIOLOGY OF ANIMALS 11 



watching shows that the Amoeba is also, with extreme slowness, 

 changing its position. This it effects by a kind of streaming 

 motion. A projection forms itself on one side, and the entire 

 substance of the Amoeba gradually streams into it ; a fresh 

 projection appears towards the same side, the streaming move- 

 ment is repeated, and, by a constant succession of such move- 

 ments, an extremely gradual locomotion, which it often takes very 

 close watching to detect, is brought about. In these movements, 

 it is to be noticed, the Amoeba is influenced to some extent by 

 contact with other minute objects ; when the processes come in 

 contact with small grains of sand or other similar particles their 

 movements are modified in such a way that the Amoeba, in its 

 slow progress onwards, passes on one side of them, so that it 

 might be said to feel its way among the solid particles in the drop 

 of sediment. 



Judging from the nature of these movements, we are obliged to 

 infer that the substance of which this remarkable object is com- 

 posed must be soft and semi-fluid, yet not miscible with the water, 

 and, therefore, preserving a sharp contour,. These and other 

 characteristics to be mentioned subsequently enable us to conclude 

 that we have to do with the substance of complex chemical com- 

 position termed protoplasm, which constitutes the vital material of 

 all living organisms whether animals or plants. In Amoeba the 

 protoplasm is in many cases clearly distinguishable into two parts, 

 an outer homogeneous, glassy-looking layer completely enclosing 

 a more granular internal mass. 



Examination of the Amoeba with a fairly high power of the 

 microscope reveals the presence in its interior of two objects which 

 with a low power we should be likely to overlook. One of these 

 is a small rounded body with well-defined contour, which 

 preserves its form during all the changes which the Amoeba as a 

 whole undergoes. This is termed the nucleus (Fig. 1, nu.) ; it is 

 enclosed in an extremely delicate membrane, and consists of a 

 protoplasmic material differing from that which forms the main 

 bulk of the Amoeba in containing a substance which refracts the 

 light more strongly and which has a stronger affinity for certain 

 colouring matters. The other minute object to be distinguished 

 in the interior appears as a clear rounded space (c. vac.) in the 

 protoplasm. When this is watched it will be observed to increase 

 gradually in size till it reaches a maximum of, let us say, a fifth of 

 the total diameter of the Amoeba, when, by a contraction of its walls, 

 it suddenly disappears, to reappear presently and gradually grow 

 again to its maximum size. This pulsating clear space is the 

 contractile vacuole. Other clear spaces which do not pulsate are 

 the non-contractile vacuoles. 



By watching the Amoeba carefully for some time we may be 

 enabled to observe that the movements of the protoplasm of the 

 body not only effect locomotion, but are connected also 'with the 



