Protoplasm. 



3 1 



In consequence the nucleus presents the apper ranee, undei 

 a low magnifying power, of a homogeneous matrix with 

 scattered granules (fig. 2). 



Usually one or more granules of larger size are to be 

 distinguished in the nucleus to which the name of nucleoli 

 has been given, some of which are probably knots on the 

 intranuclear network. 



A mass of protoplasm possessed of these morphological 

 characters may be ' naked ' or without a cell-wall, and in 

 that condition has a more or less irregular outline (fig. 3), 



FIG. 3. Amxba. polypodia. (Max Schult/e.) 



, nucleus ; Pv, contractile vacuole. 



or it may be inclosed in a definite envelope or cell-wall, 

 composed of substances formed from the protoplasm. Most 

 cells when first formed are ' naked.' They may remain so 

 during their whole existence, or they may become en- 

 veloped by a cell-wall of variable thickness and form. The 

 cell-wall is much more extensively developed in the plant 

 than in the animal organism (fig. 4). 



Physiology of protoplasm. Protoplasm and the various 

 structures differentiated from it may be considered, how- 

 ever, from another point of view. 



