218 SUMMARY OF CURRENT RESEARCHES RELATING TO 



avoided, and every looj) and filament shown in its exact arrangement, 

 length, and f(jrm. 



An account of the quantity of literature that has accumulated 

 around the discussion of tliis subject is next given, and this is 

 followed by a statement of the present condition of our knowledge of 

 cell-division, of which the following arc the more important points. 



Indirect or karyokinctic cell-division is accompanied by a meta- 

 morphosis of the cell-nucleus, which consists in the formation of a 

 figure — nuclear figure — composed of filaments ; there is an acliromatic 

 figure, or nuclear sjiindle, and a chromatic figure. The former is 

 composed of the substances of the nucleus (Flemming), or rather of the 

 cell-body (Strasburger), which are not stained by the specific nuclear 

 colouring matters, and forms a bundle of, ordinarily, spindle-shaped 

 form, which connects the two fissive poles of the cell ; from the ends 

 of the spindle rays pass out into the cell-substance. The latter is 

 formed of the colourable substance of the nucleus, and, during 

 division, undergoes a regular series of formations. At first the whole 

 chromatic substance is found in a filament which traverses and forms 

 close irregular coils in the nucleus. As the filaments become 

 gradually shorter and thicker, the loops get less numerous, and the 

 filaments then break into segments ; all these various formations are 

 comprised under the name of the coil-form of the mc^ther-nucleus. 

 The filamentar segments now aggregate towards the equator of the 

 nucleus, and around the middle of the achromatic filamentar bundle, 

 and they become looped in such a way that the figure is stellate. 

 This is succeeded by the equatorial-plate stage, which is caused by the 

 sister halves of every loop, or those formed by longitudinal cleavage, 

 separating from one another and passing to either pole. The two 

 halves of the chromatic figure again take on a stellate form, and we 

 have the daughter-stars of Flemming. The latter author has given 

 the following scheme of the chief phases of nuclear division : 



Mother-nucleus. Daughter-nucleus. 



1. Coil-form (Spirem). 5. Coil-form (Dispirem). 



4 2. Star-form (Aster). | 4. Star-form (Dyaster). 



-» 3. Phase of change (Metakinesis). 



In the above account Eabl has chiefly followed Flemming. 



liabl's own observations on these ditferent phases are then de- 

 scribed and discussed in very great detail ; and the resting stage is 

 next considered. 



The study of the structure and vital phenomena of the cells 

 shows us better than anything else the defective condition of our 

 knowledge ; we find in the nucleus and in the cells special structures, 

 and we do not know what they are for ; in division we see most 

 remarkable figures api)ear, and we are ignorant of their significance ; 

 indeed, we are not yet in a condition to give a definite answer to the 

 question what is the cell-nucleus. Yet everything shows that some 

 great law lies at the bottom of the phenomena which go on in that 

 small structure that we call a cell ; very much the same kind of 

 process is observable not only in animal and vegetable cells, but in 



