SPECIAL MORPHOLOGY OF THE PROTOZOAN NUCLEUS 



247 



centrosome and spindle-figure in which central spindle, mantle-fibres, 

 and astral rays can be distinguished. (2) Forms with centrosome and 

 spindle-figure in which astral fibres are present, but no distinction 

 between central spindle and mantle-fibres can be seen. (3) Forms 

 without centrosome, -but with a spindle-figure which cannot be resolved 

 into mantle-fibres and central spindle. 



In all of these cases the granular chromatin of the resting nucleus 

 is arranged in the form of a reticulum upon a linin network, and, with 

 few exceptions, the prophases of division are similar, in that the 

 granules are brought together and concentrated in the form of deeply 



Attraction-sphere enclosing two ccntrosomes. 



Nucleus 



Plastids lying in the 

 cytoplasm 



Vacuole 



Passive bodies (meta- 



plasm or paraplasm) 

 suspended in the cy- 

 toplasmic meshwork 



Fig. 133. — Diagram of a cell. Its basis consists of a meshwork containing numerous minute 

 granules {microsomes) and traversing a transparent ground-substance. [WILSON.] 



staining rods, the chromosomes, which are of definite number, shape, 

 and size for each species. Finally, the nuclear membrane disappears 

 and the chromosomes are left naked in the cytoplasm and connected 

 by spindle-fibres with the two poles of-the mitotic figure. 



As the variations in the three types have mainly to do with the 

 achromatic structures, further mention of the chromatin changes may 

 be omitted. In the first type considered, the approach of division is 

 signalized by the division of the centrosome into two daughter- 

 centrosomes connected by fibres which form a small spindle called 

 by Hermann ('91) the central spindle. This continually enlarges as 

 the centrosomes diverge, other fibres (mantle-fibres) meantime grow- 



