278 THE AMERICAN MONTHLY [Aug. 



PART V. NUCLEAR DIVISION.* 



25. Karyokinesis.j — After the forms and functions of 

 the cell have to some extent been enquired into, the biolo- 

 gist should attempt to become acquainted with the 

 structure and activities which have become known in re- 

 gard to the nucleus itself. Of late years a very great 

 amount of attention has been directed to the study of the 

 nucleus, and a great deal has been found out that was 

 entirely unknown even so recently as ten years ago. 

 This has been the result of improved technique, and of 

 the improved objectives. 



At first the section as a whole should be studied so as 

 to locate the cells, then the nuclei should be closely 

 examined with the highest magnifying power you can 

 command till they can be clearly distinguished into two 

 sorts: (a) the resting nucleus {p) the active nucleus. The 

 resting nuclei are likely to be in the majority, they re- 

 semble the nuclei of ordinary fully differentiated colls. 

 In them recognize : (1) the nuclear menibrane, a fine un- 

 bounding line ; (2) the chromatine, deeply stained grains 

 scattered through the interior of the nucleus ; (3) the 

 achro?natine, the non-stained remainder of the content of 

 the nucleus. Make an indexed drawing of several rest- 

 ing nuclei. 



The dividing nuclei will be seen in various stages of 

 the act, and various drawings should be made in a series 

 to show the different steps of the process according to 

 your idea of them. In the most favorable cases where 

 the act is well advanced you will recognize a great un- 



*Favorable material is furnished for nuclear study from almost any 

 developing tissue, either animal or plant, the growing tips of union 

 roots, the spermary of the Cray-Fish, developing eggs of fish and other 

 animals are among the suitable objects for this work. The material 

 must be very carefully fixed with Flemming's fluid, then stained, and 

 very thin sections cut from material imbedded in parafifine. 



tSee Wilson, Atlas of Fertilization. Macmillan, 1896. 



