242 THE PHENOMENON OF 



which ordinarily exist in Sp. nitida, at this period retain 

 their course wholly uninterrupted. The two nuclei now 

 gradually separate from one another, the mass of mucilage 

 still enveloping and connecting them becoming at the 

 same time drawn out lengthways, and finally lost in 

 longitudinal mucilaginous cords running between them ; 

 an accumulation of granular mucilage often remains mid- 

 way between the two. Contemporaneously with the 

 separation of the new nuclei progresses the division com- 

 mencing at the periphery, and by no means as a coarse 

 constriction or folding, but in the form of an extremely 

 delicate incision, continually advancing deeper into the 

 cavity of the cell, with the sharp edges of the surfaces of 

 section reaching close up to the membrane of the mother- 

 ed], without being rounded off or separated by an 

 annular intercellular passage. In cases where the dis- 

 tance of the two nuclei equalled once or twice their 

 shorter diameter, the separation penetrating from the 

 periphery extended scarcely to a sixth part of the diameter 

 of the cell ; where the nuclei were removed to a distance 

 of about four times their diameter, I found the division 

 advanced to fths, so that the part still open of the con- 

 nection between the two daughter-cells, was limited to 

 3th the original diameter. The process of this gradually 

 incising partition of the daughter-cells can hardly be 

 otherwise explained, than through a gradually progress- 

 ing formation of two plates of the primordial utricle, 

 gi'adually shutting off the daughter-cells, these plates 

 starting from the line of limitation which has made its 

 appearance in the primordial utricle of the mother-cell, 

 and advancing towards the centre of the faces of contact 

 of the two daughter-cells. If we cause contraction of the 

 primordial utricle, and loosen it from the cell-membrane, 

 by the application of acids, in these cells also, which are 

 not yet completed, the walls of the incision retreat from 

 each other, to that the mass of contents enclosed by the 

 primordial utricle in such cells, appears constricted in 

 the middle by a widely opened groove, mor,e or less deep 



