NUCLEI OP ANIMAL AND VEGETABLE CELLS. 135 



tumn, giving place to a paiicinucleolar state during spring and 

 winter. Again, it cannot be merely a phenomenon of the fission 

 of nuclei, since it is seen in nuclei which are not about to 

 divide {e.g. of red blood-corpuscles), or in those which are 

 about to disappear [e.g. of the upper layer of epidermic 

 cells). In the larva of Musca vomitoria the layers of cells 

 which, in the pupa stage, undergo histolysis are just those 

 which are characterised by an extraordinary growth of nu- 

 cleoli. Hence it is, perhaps, not impossible that in many 

 cases the multinucleolar condition may be a vain effort of 

 nature in obedience to tendencies which have long since 

 ceased to be of use, and the aims of which are only here and 

 there fully realised, as in the case of Musca vomitoria. 



We are now in a position to understand Auerbach's views 

 respecting the origin of nuclei. According to him they first 

 appear as clear spaces — vacuoles filled with a tenacious fluid 

 mass — possessing no distinct wall. Each droplet then ac- 

 quires a membrane by differentiation of the inmost layer of 

 the cell-protoplasm, and nucleoli and intermediary granules 

 afterwards make their appearance. Once differentiated the 

 nuclear membrane is an integral part of the nucleus, con- 

 stituting the latter a true vesicle, isolable as a whole by 

 mechanical means. 



Many facts speak for the identity of nucleolar substance 

 and cell-protoplasm. In optical appearance nucleoli and the 

 substance of young cells agree together. Vacuolation may 

 occur in either, large nucleoli being seldom free from clear 

 spaces. Both are ameeboid, the movements in nucleoli having 

 been described by many observers.^ Lastly, nucleoli have, 

 as Auerbach himself shoAvs, that characteristic of vital 

 protoplasm, the power of multiplication by division. In 

 other Avords, nucleoli have all the capabilities of elementary 

 organisms, and are in truth cytodes. Regarded in this light, 

 they are real daughter cells which have arisen by an 

 endogenous process; and the nucleus is the chamber 

 in which they develops. It is now merely necessary for 

 them to find a way out through the body of the mother-cell 

 in order to begin life as independent beings. 



That this method of increase has become obsolete in the 

 cases of a majority of cells of higher adulf animals, or perhaps 

 only occurs in pathological processes, may be quite true with- 

 out offering any obstacle in the way of such a hypothesis. 

 In the specialisation of function which appears as we ascend 



* Metschnikoff (Virchow, 'Archiv,' Bd. xli). Balbiani (Keferstein, Jah- 

 resber. f. 1865, in 'Zeitscb. f. rat. Med.,' xxvii. La Valette St. George 

 (Max Schultze's 'Arch.,' Bd ii). 



