THE CELL 313 



evidently due to the lack of nutrition. The cytoplasm retains 

 its irritability and responds to stimuli; the pseudopodia may 

 still be formed or the cilia continues to move, as the case 

 may be, but food particles are no longer ingested, and those 

 contained in the food vacuoles are no longer digested. The 

 cytoplasm seems to have lost the function of assimilation and 

 consequently starves. 



681. These experiments indicate that the animal functions, 

 irritability and contractility, are functions of the cytoplasm. 



682. On the other hand, from what has just been said, it is 

 seen that the nucleus has to do with the function of assimilation. 

 This is further evident in many cases in which cells are especially 

 active in the absorption of food. In such cases the nucleus is 

 prolonged into curious finger-like processes on the side of special 

 activity. In other cases the nucleus shows evidence of special 

 activity where secretory processes are prominent. Here its 

 surface also projects toward the point of activity. Since assimi- 

 lation and secretion are two phases of metabolism it is natural 

 that both should be controlled from the same source, and that 

 the nucleus should present similar appearances in both cases. 

 In addition to the control of metabolism the nucleus also has 

 the function of cell division or reproduction.. 



683. Cell Division. — The process of cell division is such a 

 complicated one, and with it are connected so many important 

 biological phenomena that it demands careful study. The first 

 evidence of preparation for cell division is seen in the rearrange- 

 ment of the chromatin. This gradually assumes a more regular 

 form. The irregular clumps and strands take on the form of 

 one or more coiled bands. These have at first an irregular out- 

 line, which gradually becomes smoother. The bands become 

 thicker and shorter and finally are seen to consist of a limited 

 and definite number of V-shaped bodies, to which the name 

 chromosomes has been given. During these changes of form 

 the affinity of the chromatin for the stains increases. At about 



