NUCLEOLAR STRUCTURES OF THE CELL. 157 



In some cases, as in the nucleolus of the egg of Polydora, 

 the vacuolar substance is distributed in the nucleolar ground 

 substance in the form of irregular canals. I believe that the 

 study of similar nucleoli misled Carnoy in his idea of a " nucleole- 

 noyau," i.e., of the assumption of a particular form of nucleolus 

 which contains all the chromatin of the nucleus in the form of 

 a looped skein, and so represents a nucleus within the nucleus. 

 That is to say, in such a nucleolus as the one jusc mentioned, 

 he mistook the network of true nucleolar ground substance 

 for chromatin, and the true vacuolar substance for the nucleo- 

 lar ground substance. Certainly in no true nucleolus of any 

 Metazoan have I seen any trace of chromatin, much less a loop 

 of chromatin ; but it is possible, though I have been unable to 

 decide the point positively, that in the Gregarines the chroma- 

 tin may be contained in the nucleoli. 



A few observers have remarked contractile vacuoles in the 

 nucleolus. 



Very frequently there may be observed, within a nucleolar 

 vacuole, one or several small granules, the nucleolini ; but as 

 far as my observations extend, such nucleolini appear to be 

 inconstant in number and occurrence, and to be merely detached 

 portions of the ground substance of the nucleolus. Accord- 

 ingly there is no good evidence for believing that the nucleolinus 

 represents the dynamic centre of the cell. 



3. Divisions, Fusions, and Amoeboid Movements in the Rest- 

 ing Cell. Divisions and fusions are normal phenomena of 

 many nucleoli. In fact, the general mode of increase in volume 

 of a nucleolus, apart from accessions to it of vacuolar substance, 

 appears to be by the addition to the surface of secondary nucle- 

 olar masses. This may be observed very clearly in the germinal 

 vesicle of Linens. In the case of the other Nemerteans ex- 

 amined by me, the nucleoli formed at the periphery of the 

 nucleus remain there for a while and increase in size, then 

 pass towards the centre, where they may either fuse first to 

 form a single large one (Stichostemma), or else immediately 

 subdivide and so produce numerous smaller ones, all of which 

 finally pass again to the nuclear membrane. In fusions of 

 nucleoli which have been formed at successive stages, and 



