REJUVENESCENCE IN NATURE. 351 



division). But there are other cases in which the re- 

 juvenising activity appears solely, or at least principally, 

 in a definite part of the mother-cell, which becomes 

 finally cut off, as a newly-formed daughter-cell, by 

 division of the contents and formation of membrane, 

 from the other relatively inactive portion, retaining un- 

 changed the properties of the mother-cell. 



The distinction of a shutting ofi" of this kind from 

 ordinary division, is especially evident whenever the 

 behaviour of the nucleus can be observed, as is the case 

 in certain examples described by Hofmeister, which I 

 shall mention hereafter. In such cases, namely, instead 

 of the formation of two new nuclei, a single new nucleus 

 presents itself in some portion of the mother-cell (often a 

 prolongation or bag-like protrusion), upon which the 

 part of the mother-cell containing the nucleus separates 

 as a distinct cell. The original nucleus remains during 

 this process in unaltered existence, or, if it has vanished 

 before the formation of the daughter-cell, no new nucleus 

 is formed in the part remaining as mother-cell during 

 the cutting-off of the new cell. Nageli* and Hofmeisterf 

 have applied to this modification of cell-division the term 

 "tying-off" (Abschniirung), a name, however, only 

 properly applicable to those cases where the daughter-cell 

 becomes externally detached from the mother-cell. Mul- 

 tiplication of cells by the formation of shut-off branch 

 sprouts likewise belongs here. 



1. The shutting-off {Abgliederung) of a daugJder-cell, 

 in the domain of vegetative cell formation. 



a. The apex of the cell is shut-off as separate cell. 



a. Withotit nucleus? Here refers the formation of 

 the mother-cell of the active gonidium, as also of the 

 motionless spore of Vaucheria, under the hypothesis, 

 that in both these cells a proper membrane is formed 

 (sharing the formation of the septum), before their 



* ' Zeitschrift/ 1847, p. 60, (Kay Traiisl., 1849, p. 131,) ' Einzell. Algen,' 

 p. 18. 



-}■ 'Enst. des Embryo der Phanerog.,' p. 61. 



