iS95. THE NUCLEOLUS. 191 



ordinary nucleolus. The grounds for this belief are certain observa- 

 tions on the micro-chemical behaviour of cells of Eqnisetnm, Psilotmn, 

 Viciafaba, Liliaceae, etc., in which it was noticed that, at the time of 

 nuclear activity, particles, some large, some small, appeared in the 

 protoplasm, and that these gave all the characteristic reactions of the 

 nucleolus. With regard to these theories of Karsten and Zimmer- 

 mann, the observations of Guignard, lately recorded in an article on the 

 origin of the attraction-spheres (9), have no small significance. The 

 centrosomes, he says, are always and invariably (in the plants 

 examined) to be found outside the nucleus, and, although at certain 

 periods of nuclear division the nucleoli may be seen lying in the 

 protoplasm in the neighbourhood of the spheres, yet nucleoli and 

 centrosomes are always distinct from one another. In the formation 

 of the spore-mother cells of Psilotmn the nucleoli, which are present in 

 numbers, were seen to find their way into the protoplasm, and then 

 to diminish in bulk, although their ultimate fate could not be made 

 out. Thus the researches of Guignard support the views expressed 

 by Zimmermann, but stand at variance with those of Karsten. 



From the foregoing it will be perceived that our knowledge of 

 the chemical, structural, and physiological relations of the nucleolus 

 is still very imperfect ; but when we recollect how extremely minute 

 this structure is, we must feel that we should not reproach ourselves 

 with this uncertainty, but rather marvel at the skill and patience of 

 those who, after all, have told us much already. Their chief praise, 

 however, is that they have started us upon a new line of research 

 which prom.ises to bring us nearer than any previous one to the 

 highest problem of biological science ; for it is indisputable that 

 within the cell lies hidden the riddle of Life, which has been a puzzle 

 to mankind through all time. 



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zelle." Inaugural Dissertation. Erlangen : 1890. 



4. Biitschli, O. — " Bronn's Klassen und Ordnungen des Thierreichs." Bd. i. 



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vol. viii. Paris : 1894. 



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