CHARACTERS OF THE NUCLEUS. 31 



as an answer to the statement, if any one were disposed to 

 make it, that in all modes of propagation of cells the nucleus 

 remains entirely passive. But in opposition to this line of argu- 

 ment is the fact that we are at present acquainted with non-nu- 

 cleated cells capable of undergoing division, which is in itself a 

 direct and sufficient answer to every statement that can be ad- 

 vanced in favour of the importance of the nucleus. It might 

 indeed be said that when the nucleus is present it fulfils some 

 important end in the act of propagation; but, in reply, it may be 

 remarked that the division of nucleated cells has been observed 

 where the nucleus has remained attached to the side. Remak* 

 has made similar statements in regard to the red blood cor- 

 puscles, and very recently Weiss-f- also in reference to the 

 protoplasm in the hairs of plants. Moreover, we know very 

 little respecting the physical peculiarities of the nucleus. 

 Reinhard has deduced its vesicular nature from its behaviour 

 in water, but we now know how little value must be placed 

 on deductions of this kind. The presence of an investing 

 membrane in many nuclei can be contested on the same grounds 

 that render the presence of an investing membrane in various 

 kinds of cells doubtful ; many nuclei appear to be completely 

 homogeneous, and are distinguishable from the surrounding 

 protoplasm only by a single well-defined contour. Nuclei are, 

 moreover, capable of undergoing manifold changes in form, and 

 these may either be of an active or of a passive nature. At 

 the same time we know that processes of budding and other 

 similar changes cannot easily be conceived to occur in a vesicle 

 enclosed by a membrane : when an amoeboid cell is pressed flat, 

 the nucleus also is compressed; and if the cell be again allowed to 

 resume its original form, the nucleus similarly changes its shape. 

 These are peculiarities that are certainly not very consonant 

 with a vesicular character ; still it is true that in many nuclei a 

 double contour can be distinctly shown, as, for example, in many 

 ganglion cells. It cannot be doubted, also, that such nuclei are 

 invested by a limiting membrane of different nature from the 

 contents ; but we have no right to draw the conclusion from this, 



* Entwickelungsgeschichte. Berlin, 1855. 

 t Die Pflanzenhaare. Berlin, 1867 



