( 137 ) 

 NOTES AND MEMOEANDA. 



Cells, and their Vital Phenomena.— Professor W. Flemming, of 

 Kiel, has published * a detailed account of his extensive researches on 

 the structure of nuclei, and their behaviour during the process of cell- 

 division. The observations were made chiefly on cells from various 

 parts of the body of the larval Salamandra ; these were examined in 

 the living state, and also after treatment with chromic acid, followed by 

 absolute alcohol, staining with safranin, and clarifying, after a second 

 treatment with absolute alcohol, with oil of cloves. H^ematoxylin 

 staining of chromic and picric acid preparations was also employed. 

 According to Flemming, the quiescent nucleus consists of — 



1. An investing membrane. 



2. An intranuclear network consisting of an extensive system of 

 ramified filaments exhibiting at intervals thickenings or pseudo- 

 nucleoli.f 



3. The true nucleoli. 



4. A pale ground-substance filling up the remaining space, and 

 devoid of visible structure in the living state, but assuming a granular 

 or fibrillar appearance by the action of reagents. 



In the process of cell-division the nucleus passes through the 

 following phases : — 



1. The somewhat coarse intranuclear network is converted into a 

 fine-meshed coil, presenting a basket-like appearance. 



2. The meshes of the coil become coarser and at the same time 

 looser. 



3. The coil assumes a wreath-like form, a space being left in the 

 centre of the nucleus free from filaments. 



4. The filaments again advance to the centre, but separate into 

 loops peripherally so as to give the whole nucleus a star-like form. 



5. The individual rays of this star imdergo longitudinal fission 

 along their whole length, producing 



6. Another star-form, distinguished from the first by the extreme 

 fineness of its rays. 



7. The star-form disappears, its filaments becoming collected into 

 a plate-like body, situated equatorially across the centre of the cell. 



The foregoing are the changes undergone by the mother-nucleus 

 preparatory to division ; the following are the stages of the daughter- 

 nuclei. It will be seen that they correspond with those of the mother- 

 nucleus, but occur in an inverse order. 



8. The equatorial plate assumes a sort of barrel-shape ; a plane 

 across the equator of the barrel is free from filaments, and marks the 

 plane of division of the nucleus ; from this plane the filaments 

 radiate, converging slightly, in two directions, or towards the original 

 bounding planes of the equatorial plate. 



9. Probably, though this is by no means certain, the filaments 



* ' Archiv f. Mikr. Anat.,' vol. xvi. (1878) p. 302. 



t This word la employed in a different sense by Van Beneden. 



