168 UTRICULAR STRUCTURES. 



dition. In them the septum is visible, as a line, only in 

 the moment of the division. If, therefore, analogy with 

 other cells does not afford evidence of the presence of a 

 membrane to these cells, we can only draw conclusions 

 in respect to it from the septum which is seen in the 

 propagation ; but when we can succeed in bringing two 

 such free cells together, in such a manner that, where in 

 contact, they are reciprocally somewhat flattened against 

 each other, the two membranes become visible at once, 

 as a septum, while at the remainder of the periphery, as 

 before the union was the case at all points, nothing can 

 be seen of the membrane. I have accomplished this in 

 Palmella, Protococcus, and Saccharomyces. 



Nucleus and cell then exhibit, in reference to their 

 membrane and its relation to the contents, the same phe- 

 nomena. In small and young free individuals, the 

 membrane and contents are not distinguishable at first 

 sight ; they do not become so until they have undergone 

 further development. In individuals, however, which 

 originate through parietal formation, the membrane is 

 evident as a septum in the earliest condition. The sole 

 distinction, following from the nature of the case, which 

 prevails between nucleus and cell is, that there are far 

 more conditions of the nucleus than of the cell, in which 

 a distinction between membrane and contents is impos- 

 sible, since the phenomena are represented on a con- 

 siderably smaller scale in the nucleus than in the cell. 



After disposing of the objections above mooted, I pro- 

 ceed to a short exposition of the vital phenomena of the 

 nuclear utricle. 



The nucleus originates in two ways : either free in the 

 contents of a cell, or by the division of a parent-nucleus. 

 If the nucleus originates by division, the phenomena 

 presented are similar to those in the division of a cell. 

 A septum becomes visible in the parent nuclear utricle, 

 dividing it into two halves (as in Tradescantia] ;* soine- 



* Niigeli on Cell-Formation. Ray Trans., 1845, p. 184, pi. vii, fig. 20. 



