144 PRINGSHEIM, ON THE STRUCTUKE 



volves only the inner layers beneath the chlorophyll-granules 

 (^Chard). The author supposes that the formative activity of 

 the cell-contents is specially seated at the line of jvinction of 

 the cell-fluid with the granular layer, and that it is the cause 

 of the motion. In cases w^here the plasma does not constitute 

 a continuous lining to the wall, it cannot, by means of re- 

 agents, be detached from the wall with a definite outline, but in 

 the shape of a variously formed net-work of streaks of plasma. 

 But when it constitutes a complete and uniform covering, it 

 contracts in a continuous form under the action of the re- 

 agent, and under certain conditions assumes the false appear- 

 ance of a membrane. Lastly, in cases where the plasma is 

 divided, even in the cell, into two distinct layers, not only 

 does the outer layer appear as a membrane, but the granular 

 layer also presents a defined boundary. Whenever powerful 

 re-agents are applied, and a rapid contraction thus induced, 

 phenomena are always manifested, which necessarily lead to 

 the assumption of the existence of a primordial utricle, 

 although many different things have been included under 

 that term. But when cells in which the primordial utricle 

 is displayed in the most distinct form are treated with weak 

 re-agents, although the same results are ultimately attained, 

 the process, owing to the more gradual way in which it is 

 effected, may be accurately observed, and it will thus be 

 seen that it is not smooth membranes which are separated 

 from each other, but a glutinous substance which is detached 

 from a membrane to which it was adherent ; the detachment 

 frequently takes place only partially, and the connexion with 

 the wall is maintained by isolated threads of plasma, which 

 become more and more attenuated or are ruptured, until, at 

 last, the outermost layer of the plasma, contracting, assumes 

 the appearance of a membrane. This slow separation from 

 the wall satisfactorily shows, in every case, that the internal 

 coating of the cell is composed of a muco-glutinous, viscous 

 substance, and that it is not, properly speaking, a membrane. 

 The same considerations also confirm the author in his opinion 

 that, when large cells are treated with slowly acting re-agents, 

 the contents surrounded by the " cutaneous layer " often con- 

 tract into two, or, more rarely, into several segments, whose 

 connective portions becoming gradually attenuated are ulti- 

 mately ruptured, and then isolated, though appearing to be 

 bounded by an equally even and sharply-defined outline, as 

 that of the whole contents previous to their division. 



In the third section the author speaks of the cell-division 

 in the Confervce, noting, in the first place, its mode of occur- 

 rence in Cladophora, and afterwards in Conferva, Spirogyra, 



