SURVEY OF CELL-LIFE. | 179 
in all cases, for, according to Schleiden, it remains persistent 
in most cells in the Euphorbiacez, and the blood-corpuscles 
may be quoted as an example to the same effect in animals. 
The fact that many nuclei are developed into hollow vesicles, 
and the difficulty of distinguishing some of these hollow nuclei 
from cells, forms quite sufficient ground for the supposition 
that a nucleus does not differ essentially from a cell; that an 
ordinary nucleated cell is nothing more than a cell formed 
around the outside of another cell, the nucleus; and _ that 
the only difference between the two consists in the inner 
one being more slowly and less completely developed, after 
the external one has been formed around it. If this descrip- 
tion were correct, we might express ourselves with more pre- 
cision, and designate the nuclei as cells of the first order, and 
the ordinary nucleated cells as cells of the second order. 
Hitherto we have decidedly maintained a distinction between 
cell and nucleus; and it was convenient to do so as long as 
we were engaged in merely describing the observations. There 
can be no doubt that the nuclei correspond to one another in 
all cells; but the designation, “cells of the first order,” in- 
cludes a theoretical view of the matter which has yet to be 
proved, namely, the identity of the formative process of the 
cell and the nucleus. This identity, however, is of the greatest 
importance for our theory, and we must therefore compare 
the two processes somewhat more closely. The formation 
of the cell commenced with the deposition of a precipitate 
around the nucleus; the same occurs in the formation of the 
nucleus around the nucleolus. The deposit becomes defined 
externally into a solid stratum: the same takes place in the 
formation of the nucleus. The development proceeds no 
farther in many nuclei, and we also meet with cells which 
remain stationary at the same poit. The further development 
of the cells is manifested either by the entire stratum, or only 
the external part of it becoming consolidated into a membrane; 
this is precisely what occurs with the nuclei which undergo 
further development. The cell-membrane inereases in its 
superficies, and often in thickness also, and separates from 
the nucleus, which remains lying on the wall; the membrane 
of the hollow cell-nuclei grows in the same manner, and the 
nucleolus remains adherent to a spot upon the wall. <A trans- 
