DEVELOPMENT OF CELLS. 1 1 



utricle, which increases in size by the assimilation of the fluid in which 

 it is placed. The development usually takes place on one side, the new 

 cell appearing in the form of a transparent vesicle rising from the 

 surface, and leaving the nucleus attached to the other side of the 

 utricle (fig. 33). The cytoblast is thus enclosed in the utricle, and may 

 ultimately disappear by absorption, leaving a non-nucleated cell. The 

 membrane surrounding the nucleus is converted gradually into cellu- 

 lose, and thus the perfect cell is formed. According to Mohl, the 

 nucleus is at first retained in the centre of the cell by means of mucous 

 threads, and afterwards becomes fixed to the sides. Occasionally, the 

 nucleus becomes imbedded in a duplication of the cell-wall. This 

 process of cell-development, according to Ascherson, is similar to what 

 takes place when oil is mingled with a mucilaginous or albuminous 

 fluid, each minute molecule of oil becoming surrounded by a thin 

 film of membrane. In this view the cell is originally of a more or less 

 globular form, and all the varieties of shape afterwards seen are due 

 to changes in the progress of growth. 



Barry affirms that a minute pellucid globule (hyaline) is first seen in 

 the formative matter. This absorbs and assimilates new matter, enlarges 

 and becomes granular, thus forming the cytoblast of Schleiden, after it 

 has prepared a nucleolus for itself. The outer part of the cytoblast rises 

 in the form of a membrane to produce a cell; another portion of it is 

 concerned in the formation of the contents of the cell; and what is left of 

 the cytoblast in the cell-wall becomes the nucleus of the cell. This nu- 

 cleus (not the cytoblast of Schleiden) remaining on the cell-waE, is not 

 absorbed, but becomes the source whence cytoblasts are formed. Tims, 

 according to Barry, the substance of the larger body is not deposited 

 around the smaller, but the smaller is transformed into the larger; the 

 nucleolus becomes the cytoblast, and the cytoblast becomes a nucleated 

 cell. 



As regards the development of cells from nuclei, the present state of 

 our knowledge does not warrant us in stating more than that there is 

 a protoplasm, or soft organizable matter, which is contained in cells, or 

 in the spaces between them ; that in this matter a nucleus is produced, 

 either around previously existing nucleoli, or from the granules of the 

 protoplasm; and that the nucleus has the power of developing new 

 cells, which become nucleated, increase in size, and escape from the 

 parent cell, by rupture or absorption. In the production of young 

 cells, the nucleus of the parent cell sometimes divides into two, each 

 part having the power of giving rise to a new cell. There is thus a 

 constant multiplication of cells by an intra-cellular or endogenous 

 (svftov, within, and yewativ, to generate) process. 



23. It is supposed by some that cells may arise without a nucleus, 

 by the simple aggregation of granular matter, which becomes enve- 

 loped in a membrane, and thus forms a cell with granular contents. 



