THE PHENOMENA OF LIFE. 13 



is now quite generally believed that the chromatin occurs as short, rod- 

 like and highly refractive masses, which are embedded in the linin in a 

 regular series. 



The nudeoli, or plasmosomes, are spherical bodies of unknown func- 

 tion. They stain deeply, and may either lie free in the nuclear matrix 

 or be attached to the threads of the network. 



Attraction Sphere. 



In addition to the nucleus, a, minute spherical body called the centra- 

 some is believed to be constantly present in animal cells, though some- 

 times too small to be demonstrated. The centrosome is smaller than 

 the nucleus, close to which it lies, and exerts a peculiar attraction for 



Fig. HA. Leucocyte of Salamander Larva, showing attraction sphere. (After Flemrning.) 



the protoplasmic filaments and granules in its vicinity, so that it is sur- 

 rounded by a zone of fine radiating fibrils, forming the attraction sphere 

 or archoplasm. Some authorities assert that the centrosome lies within 

 the nucleus in the resting state, and only passes into the cell proper in 

 the earlier stages of cell division. The attraction sphere is most dis- 

 tinctly seen in cells about to divide. It plays an important role in 

 nuclear division, but it is doubted if it gives the initial impulse to the 

 process. 



Cell Division. 



The division of a cell is preceded by division of its nucleus, which 

 may be either direct or indirect. Direct or simple division, amitosis or 

 akinesis (xivyais, movement), occurs without any change in the arrange- 

 ment of the intranuclear network; it is probably limited to the amoebae. 



