16 MANUAL OF ZOOLOGY sect. 



to some extent by contact with other minute objects; when 

 the processes come inicontact with small grains of sand or 

 other similar particles, their movements are modified in such 

 a way that the Amceba, 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 a drop of sediment. 



Judging from the nature of the movements, we are obliged 

 to infer that the substance of which this remarkable object is 

 composed 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 composition termed protoplasm, which 

 constitutes the vital material of all living organisms whether 

 animals or plants. In Amceba the protoplasm is clearly dis- 

 tinguishable 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 of a homogeneous appear- 

 ance, which preserves its form during all the changes which 

 the Amceba as a whole undergoes. This is termed the 

 nucleus (Fig. i, nil) ; it is enclosed in an extremely delicate 

 membrane, and consists of a protoplasmic material differing 

 from that which forms the main bulk of the Amceba in con- 

 taining 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 



