SURVEY OF CELL-LIFE. 179 



in all cases, for, according to Schleiden, it remains persistent 

 in most cells in the Euphorbiaccie, 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 resides, 

 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 point. 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 increases 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- 



