i 

 44 THE CELL DOCTRINE. 



" 77. I am very much inclined to believe, that in 

 the many instances in which authors on ' cells' have 

 described and figured more than one nucleolus in a 

 nucleus, there has been either an incipient division 

 of the nucleus into discs, or the nucleus has consisted 

 of two or more discs; the nucleoli of those authors 

 having been the minute and highly refracting cavi- 

 ties or depressions in the discs. If this has really 

 been the case, it affords additional evidence, I think, 

 that reproduction of cells by the process I have described 

 namely, division of the nucleus of the parent cell is uni- 

 versal so numerous have*been the instances in 

 question. I may refer to the figures given by 

 Schwann, who examined nearly every tissue, and to 

 those of Schleiden, whose observations have been so 

 extensive on plants. I think, indeed, that many of 

 the figures of Schwann afford evidence of the divi- 

 sion in question having taken place. It is to be 

 recognized in his delineation of the cells of cartilage, 

 cellular tissue, middle coat of the aorta, muscle, 

 tendon, the feather, &c. The same remark is appli- 

 cable to a figure given by Reichert of ciliated epithe- 

 lium cells. Dr. Henle found that in the layers of 

 his ' pilaster-epithelium ' cells, the nucleus, very dis- 

 tinct in the lower cells, had almost disappeared in 

 those situated in the upper part. From this obser- 

 vation, and from the presence of two nucleoli in some 

 of the nuclei figured by this observer, as well as from 

 the nucleus becoming more granular, I think it ex- 

 tremely probable that these cells (including those of 

 the epidermis), are reproduced by the process just 

 referred to division of the nucleus; additions being 



