in the Inteiior of Cells. 5 



entire mass between two glasses, without the least trace of a 

 surrounding membrane being detectable. On the other hand, 

 an internal movement begins sometimes to be perceptible in 

 the protoplasma even at this period, which does not, it is true, as 

 yet possess the form of a distinct current, but produces a slow 

 change in the form and position of the cavities above-mentioned ; 

 thus likewise indicating that they are not cell-spaces inclosed by 

 a membrane, but vesicular cavities in a viscous fluid. 



The older the cell becomes, the more do the spaces filled with 

 this aqueous sap increase in size in proportion to the mass of 

 protoplasma. In consequence of this the cavities run into one, 

 and the viscous fluid now forms, instead of perfect septa, only 

 more or less thick filaments, which radiate from the mass sur- 

 rounding the nucleus like an atmosphere towards the cell-wall, 

 where they turn back, and unite to form retrogressive filaments, 

 and in this manner form a more or less ramified anastomosing net- 

 work. When the cells lie one above another in longitudinal series, 

 as in the simple articulated hairs for instance in Tradescantia, the 

 chief mass of these filaments, united into a thick cord, mostly pro- 

 ceeds in the axis of the cell from the centre of the one diagonal 

 wall of the cell to the centre of the opposite diagonal wall, and 

 inclose the nucleus in the middle of the cell on all sides. Where, 

 on the contrary, the cells lie together in masses, the filaments 

 generally radiate from the central nucleus towards all sides uni- 

 formly. There is however no general rule in this respect ; thus 

 for instance, in Zi/gnema, notwithstanding the bead-like appo- 

 sition of the cells, the nucleus is suspended to filaments which 

 radiate on all sides without any particularly thick and numerous 

 filaments proceeding through the axis of the cell. 



It may perhaps not be superfluous to draw attention to a phe- 

 nomenon which I am not yet able to explain. At the period 

 when the previously isolated cavities begin to flow together the 

 cell acquires a very peculiar appearance, resulting from the dif- 

 ferent refracting powers of the substances contained in it. The 

 spaces, for instance, situated in the protoplasma frequently ap- 

 pear, not as if they were cavities filled with a thin aqueous 

 liquid, but as if they consisted of masses of a semi-fluid sub- 

 stance, refracting the light more strongly than the surrounding 

 protoplasma. Except in the absence of colour, they look very 

 much like the red masses which are contained in the cells of 

 Bang ia atropurpurea. This appearance subsequently changes, 

 and frequently under the eyes of the observer, when the cells are 

 placed in water, and these places are then readily perceived to be 

 cavities which arc filled with an aqueous liquid. Now whether 

 at the time when they resemble solid masses a substance is dis- 



