REJUVENESCENCE IN NATURE. 243 



according to the degree of division. By this means also 

 we may satisfy ourselves that the secretion of cellulose 

 in the notch of the primordial utricle begins before the 

 termination of division, consequently that the septum is 

 originally an annular ridge, not reaching to the middle. 

 I could already distinguish its rudiment in cases in which 

 the notch occupied about Jth of the diameter. Extremely 

 thin and delicate as the septum is in its earliest rudi- 

 ments, it separates completely from the walls of the 

 retreating notch of the primordial utricle, and appears 

 as a ridge attached at right angles on the cell-wall, 

 without an intercellular passage, diminishing to inappre- 

 ciable thickness at the bottom of the notch. That the 

 contents of the two daughter-cells are not merely appa- 

 rently (by adherence of the two portions to a septum 

 thinner in the middle), but really directly connected, in 

 these stages of transition, follows, not only from the 

 already described connection of the two nuclei by the 

 mucilaginous mass drawn out into a filament, but also 

 from the behaviour of the spiral chlorophyll bands. As 

 soon as the peripherical groove has attained a distinguish- 

 able depth, an interruption of the regular course of these 

 bands takes place ; they become pushed forcibly into the 

 interior of the cell at the point of transition, becoming, at 

 the same time, loosened from the primordial utricle for 

 some distance from the notch. The more they are bent 

 into the centre of the cell, the more they are attenuated 

 at the point of transition, till at length the connection is 

 dissolved. I could trace their uninterrupted course from one 

 cell to the other distinctly, even in cases where the diameter 

 of the isthmus did not amount to more than ^th of the 

 diameter of the cell. After the division is completed, 

 the position of the nucleus remains excentrical for some 

 time longer, nearest to the newly formed wall ; but it 

 soon retreats to the middle of the cell, the mucilaginous 

 filaments radiating from it, which were at first directed 

 in greatest number and thickness to the newly formed 

 septum, finally run principally to the lateral walls of the 



