SPECIAL MORPHOLOGY OF THE PROTOZOAN NUCLEUS 2JJ 



improbable that the condition of the distributed nucleus, as found in 

 Tetramitus, may have been widely spread among the lower forms of 

 life. In Tetramilus the division-centre becomes more compact, and 

 distinct during the preparatory division stages, while the chromatin 

 granules collect in a small aggregate in its immediate vicinity. The 

 sphere then divides and the chromatin aggregate separates into two 

 portions. This stage of the division probably corresponds with the 

 stage described by Schaudinn in Paramceba, where the chromatin 

 granules form a ring about the divided sphere. The swarm-spores 

 increase by simple division, as in Tetramitus, and a dumb-bell struc- 

 ture results. The nucleus, which is a well-defined body, then moves 

 around the connecting strand of the daughter-centres until it sur- 

 rounds it as the nucleus of Noctiluca surrounds the central spindle 

 (Fig. 142, F, G}. The connecting strand of the daughter-centres of 

 Paramceba is analogous, therefore, to the central spindle of Noctiluca 

 and of the Metazoa. 



It is a temporary stage like this in Tetramitus or Paramceba, that 

 lends plausibility to Schaudinn's other alternative, although the 

 reverse view may also be conceived, the diffusion of the chromatin 

 granules taking place by reason of the disappearance through gradual 

 degeneration of the nuclear membrane. If the latter view of the origin 

 of diffused chromatin be accepted, then the theory of the original 

 intra-nuclear position of the sphere, for which there are certainly a 

 great many supporting facts, is warranted. There is considerable 

 evidence, on the other hand, to support the argument that the 

 division-centre was originally a distinct cytoplasmic structure, which 

 only secondarily became connected with the nucleus (e.g. Tetramitus 

 and Paramceba}. Intermediate stages between the temporary stage in 

 Tetramitus and Paramceba, and the permanent intra-nuclear division- 

 centre, may be seen in numerous Flagellidia, such as Chilomonas and 

 some species of Trachelomonas, where no nuclear membrane surrounds 

 the chromatin granules. Even in these low forms, the sphere appar- 

 ently exerts some force of attraction, perhaps chemotactic, upon the 

 chromatin, and this may or may not be strong enough to keep the 

 granules permanently aggregated. If not, the distributed nucleus may 

 result ; if so, the intra-nuclear condition of the sphere is the outcome. 

 In Paramceba, Noctihica, in diatoms, and in the majority of Metazoa 

 and plants, a nuclear membrane is formed and the sphere remains in 

 its cytoplasmic or extra-nuclear condition, and, as a cytoplasmic body, 

 or as a kinetic substance (archoplasm or kinoplasm), may undergo fur- 

 ther differentiations leading to the complicated mitotic figures of 

 higher animals and plants. In the majority of cases the nuclear 

 membrane disappears during mitosis, and the primitive conditions are 

 thus repeated. By rupture of the membrane, the substance of the 



