18 



PSYCHOBIOLOGY 



along the linin fibers. The distribution of the chromatin is in all cases 

 essentially modified during the process of mitotic cell division, as described 

 below. Of the function of the nucleolus, practically nothing is known. 



There are three characteristic ways in which new cells are produced by 

 preexisting ones. 1. Budding. [Fig. 4.] The new cell grows directly 

 out of the old one as a twig grows out of a limb. In this case the parent 

 cell apparently retains its identity, and we can speak of the new cell as 



Fig. 6. Diagram of several successive stages in karyokinesis (mitotic division). 

 (Schafer, Microscopic Anatomy.) I. shows the 'resting' cell, i. e., the cell before 

 the commencing of mitosis. VIII. shows mitosis virtually complete, the two new 

 cells being in the ' resting ' condition. 



the daughter cell. The daughter cell is partially formed from the cyto- 

 plasm of the parent cell, and then a portion of the parent nucleus is 

 separated from the remainder and passes into the daughter cell. 2. Fis- 

 sion, or direct division [Fig. 5]. The cytoplasm and the nucleus divide 

 by progressive constriction, beginning in the nucleus so that two daughter 

 cells are formed, half of the old nucleus going to each. 3. Mitosis, indi- 



