THE CELL AND CELL DIVISION 39 



mass called the centrosphere or attraction sphere immediately 

 surrounds the centrosome, and peripherally, radiating from 

 this out into the cytoplasm, there is at times a collection of 

 diverging rays or fibers called collectively the aster. In the 

 ordinary vegetative cell the centrosome and archoplasmic 

 structures are usually reduced in size and perhaps even absent 

 in some cells, but in the dividing cell they may be very large 

 and prominent organs extending nearly throughout the cell, 

 for their chief function is in connection with the process of 

 cell division. Similar dense granules and fibers are found as- 

 sociated with organs of the cell which are motile, for example, 

 the granules at the bases of cilia and flagella, the axial fila- 

 ments of some flagella, undulating membranes, and some 

 pseudopodia, the fibrillse of muscle cells, etc. All such modi- 

 fications of protoplasm connected particularly with the pro- 

 duction or regulation of motion are included under the general 

 term kinoplasm (Strasburger) . It has been suggested that 

 the kinoplasm of the cell is of the nature of a definite and 

 permanent cell organ. In many cells the centrosome is such 

 a permanent organ, but many other kinoplasmic structures 

 seem to be more or less temporary and may disappear or 

 be formed anew at the time of cell division or at other times. 

 The rays of the aster, for example, in many cases apparently 

 are formed from the enlargement and rearrangement of the 

 cytoplasmic reticulum resulting from the activity (probably 

 chemical) of the centrosome. 



In addition to these nearly constant cell structures of com- 

 paratively uniform characteristics, there are various other 

 organs or bodies which are peculiar to certain special kinds 

 of cells. Among these are the bodies called in general plastids 

 (Fig. 14, IV), of which the more familiar are the pigment bodies, 

 such as chloroplastids or chlorophyl bodies, the chromoplastids 

 or colored bodies not containing chlorophyl, amyloplastids or 

 starch-forming bodies, protein-forming plastids, and others. 

 Vacuoles of various sizes and kinds are very common, such as 

 the digestive, excretory, food, water, and food-storage vacuoles; 

 occasionally one or more are specialized as contractile or pul- 



