UTRICULAR STRUCTURES. 165 



called utricles, because the utricles, according to their 

 definition, are to be described neither as hollow spaces, 

 nor as hollow spaces surrounded by a membrane. They 

 must at least possess a special membrane and contents 

 subject to special metamorphoses. 



1. Nuclear Utricles, Nuclei. 



That the nuclei are utricles I have pointed out in an- 

 other place.* I then brought forward the following 

 reasons in favour of this opinion : 



1. When the nucleus admits of minute examination, 

 in respect of size and density, a membrane, and contents 

 distinct from this, may always be recognised. The mem- 

 brane is only overlooked where the nuclei are too small, 

 or where dense contents are inclosed in a delicate mem- 

 brane. In the latter case, it is sometimes possible to 

 render the membrane visible by the action of re-agents. 



2. The membrane is different from the contents (by 

 no means the outermost layer of them) ; it is not coloured 

 by iodine and is composed of gelatine, while the con- 

 tents are usually coloured brown by iodine and consist of 

 mucilage. 



3. The contents exhibit peculiar transformations, which 

 are analogous to those of the cell-contents. 



4. The membrane is proper to the nucleus (by no 

 means a mere deposit from the cell-contents), as is proved 

 by the propagation of the nuclei, which exhibits the same 

 phenomena as the propagation of the cells. 



I may add here that the membrane of the nucleus may 

 sometimes be recognised very distinctly, when it becomes 

 expanded through endosmose of water, f 



Schleiden \ thinks " that the nuclei become hollow 



* Schleiden und Nageli, Zeitsch. f. wiss. Bot., i, p. 68 ; Ray Trans. 1845, 

 p. 246. 



+ See p. 110 of this volume, pi. ii, fig. 9, , k, I, m. 



J Grundziige, second edition, i, p. 199. Schleiden reproaches me for an 

 unsettled terminology. I have called the nucleus an utricle (blascheri), and 



