CELL FORMATION. 533 



coat of the eye, the lamina fusca, as it is called. The cylin- 

 drical form of cell is found with delicate processes shooting 

 out from the broad end* these are called ciliated, seen at 

 fig. 274, d, and the cilia are endowed with the power to move 

 spontaneously, having a vibratile motion, intended to urge 

 on the secretions of the part in a particular direction.. 



Change of the Nucleus. Fig. 269, No. 1, 2, 3, and 4. 

 The nucleus may undergo a change; it maybe smooth, 

 round, compressed, like the cell to which it belongs; it 

 may disappear altogether, and the cell which contained it 

 remain. The corpuscles of the blood and the epidermic 

 scales in the last stage of development are examples. The 

 contents may change with the membrane itself Some 

 cells are filled with a granulous matter, others with pig- 

 ment, or colouring-matter, as the cells of the choroid of 

 the eye. Others, again, become filled with matters which 

 form the secretions; the cell-membrane breaking, and 

 pouring out its contents. The cell-membrane may become 

 so changed, as to be of a horny consistence, not capable of 

 being acted on by acetic acid, as it could have been before ; 

 this is well seen in the last changes of the epidermoid and 

 epithelium scales. 



In some cases the walls of the cell increase in thickness. 

 (Fig. 269, No. 5.) Under the microscope, some cells 

 appear to be composed of concentric laminae. In plants 

 this is the common mode of increase in the thickness of 

 the cell, but the deposit does not take place entirely 

 around, but only here and there, so that vacant spaces 

 are left which form canals, and may become branched, 

 these canals are named pore-canals. (Fig. 269, No. 6.) 

 They do not perforate the outer layers, consequently the 

 blind ends are seen through the outer membrane, and 

 were supposed, indeed, to be apertures ; but they are not 

 so. Henle thinks he has found canals in such cells in 

 animals, similar to those in vegetables in the cartilage of 

 the epiglottis, for instance. Another mode of development 

 is, that the cells may not remain free and independent, 

 but may coalesce with each other. (Fig. 269, No. 7.) Of 

 this there are two modes the first is, before coalescence, 

 the cell may have attained its full development as a cell ; 

 secondly, when coalescence occurs, the cell may be simply a 



