REJUVENESCENCE IN NATURE. 241 



position, and draws it to the side, through the contraction 

 and partial tearing up of the radiating mucilaginous 

 threads fixing it in the cavity of the cell. Before the applica- 

 tion of iodine it has a homogeneous aspect, and the line 

 of demarcation between its body and the surrounding 

 mucilaginous envelope running out into radiating fila- 

 ments, is difficult to see ; on the application of spirit the 

 outline becomes clear, and the interior acquires a granular- 

 punctate aspect ; the large nucleolus always existing also 

 appears punctated in the interior. The nucleus is some- 

 what lenticularly compressed in relation to the longi- 

 tudinal axis of the cell, its larger diameter amounting, in 

 Spirogyra nitida, on an average, to about gjd, that of the 

 nucleolus T ^ 5 th millim. The size of both increases some- 

 what during the ulterior development, and most con- 

 siderably just before the commencement of the division 

 of the cell, at which time its lenticularly-abbreviated 

 shape is also somewhat elongated. I have not been able 

 to make out clearly whether there is a division of the 

 nucleus here, or a solution of it followed by the formation 

 of two new nuclei, or how the nucleoli behave in this 

 doubling. When the cell is near to division, two new 

 nuclei present themselves in place of the original, con- 

 siderably smaller than it, and with proportionate nucleoli. 

 The two new nuclei touch at first, but I never saw them 

 lying flat upon one another, as if produced by division ; 

 they always had rounded surfaces. The circumstance that 

 the two new nuclei are surrounded by a common, abundant 

 mucilaginous envelope, not existing previously, seems to 

 me to speak rather for a solution of the original nucleus, 

 than for a division of it. Simultaneously with the appear- 

 ance of the two new nuclei, we discover an extremely 

 delicate line upon the surface of the cell-contents, indi- 

 cating the division now beginning also at the periphery ; 

 this line is, however, so delicate at first, that when we 

 have the margin of the cell in focus, no trace whatever 

 of a grooving or constriction of the primordial utricle can 

 be detected, and the spiral chlorophyll bands, three of 



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