igo NATURAL SCIENCE. Sept.. 



(or in the protoplasm), may be derived from the nucleolus ? These 

 are at present open, although much-discussed questions. 



Some have thought that the nuclear-spindle owes its origin to 

 this vanished structure, others, and perhaps the majority, including 

 Flemming (7), Juranyi (14), and Went (27), are of opinion that there 

 exists a direct connection between the nucleolus and the chromo- 

 somes. Strasburger (24) also sees a connection between these two 

 things, but not a direct one. The nucleolus, in his belief, is dissolved 

 in the liquid portions of the nucleus (nuclear-sap), and part of it may 

 then serve as a food-stuff to the chromosomes, and be absorbed by 

 them whilst the rest remains behind in solution. When the daughter- 

 nuclei are formed, the nucleolar substance collects together from the 

 threadwork and from the nuclear-sap to form fresh nucleoli. Since, 

 as has been pointed out above, we have very good reason to believe 

 in the dissimilarity between the materials of the chromosomes 

 (nuclein) and the materials of the nucleolus, it is not easy to see how 

 any such relations can exist between the two. 



Zacharias (30) has watched the disappearance of the nucleolus 

 from the cells of Chara, in which he noticed that it loses its definite 

 outhne and changes its shape in slow amoeboid movements, becoming 

 at the same time diminished in size, finally to vanish altogether. He 

 thinks that it is probable that the more easily soluble proteid con- 

 stituents of the structure are dissolved, whilst the plastin framework 

 remains intact, but hidden by other plastin elements in the dividing 

 nucleus. 



Of late days, much attention has been given to those structures of 

 the cell spoken of as attraction-spheres and their central-particles or 

 centrosomes. 



The exact life-history of these organs of the cell, for so we may 

 term them, is not yet ascertained, but much speculation has been rife 

 in connection with it. Only one of these hypotheses will interest us 

 in the present article, it is the one recently propounded by Karsten 

 (15). In studying certain cells of Psilotnm he found, at the time of 

 division, the nucleoli, of which there may be several, lying close to 

 the periphery of the nucleus and, on the absorption of the nuclear- 

 membrane, two nucleoli passing out into the protoplasm and taking 

 up their positions at the poles of the nucleus. He further asserts that 

 in some cases he was able to detect a distinct radiation around each 

 nucleolus, and from these observations he concludes that the nucleoli 

 give rise to the centrosomes of the attractioa-sphe res, and are sub- 

 sequently re-formed into the nucleoli of the daughter-nuclei. 



Another theory of considerable interest, and of recent date, is 

 that of A. Zimmermann (32). In the opinion of this observer, the 

 nucleoli wander out of the nucleus at the time of division and find 

 their way into the protoplasm as bodies of varying size; when 

 nuclear division has taken place, it is probable that the nucleoH travel 

 back to the daughter-nuclei and once more fuse together into the 



