CELLS OF TRANSITION. 217 



sists of a vesicle constructed of a fine simple transparent cell- 

 membrane filled with granular matter, and containing a vesi- 

 cular nucleus witli one or more nucleoli. Their diameter varies 

 from the 300th of an inch to less than 1-1 Oth of that measure, 

 so that some hardly equal the size of an ordinary red globule 

 of the blood. Their function is of the most important char- 

 acter they plainly constitute the means of communication 

 between the several nerve-filaments or nerves, and originate 

 that signal force by which the sensitive and motor processes of 

 the nervous system are carried on. 



4. Adipose-Cells. The adipose-cells, into which the oily and 

 adipose matter is secreted, are the largest cells in the body. 

 Owing to the pressure to which they are often subjected, they 

 are apt to assume a polygonal form. 



5. Pigment-Cells. Pigment-cells, within which are produced 

 in a fluid or granular form the various coloured substances 

 that colour different textures of organic bodies, present, as 

 might be anticipated, remarkable variations of size and shape. 



6. Glandular or Secreting Cells. In the function of secre- 

 tion, taken in its largest sense, cells very various in character 

 perform an important part. Such cells draw from the blood, 

 some bile, some urea, some saliva, some milk, and some even 

 the germs of new blood-corpuscles, and no explanation can be 

 given of this surprising result. The process of secretion, 'in 

 which the cell-structure uniformly takes part, is an ultimate 

 fact in physiology that is, one of which no explanation has 

 been as yet discovered. 



7. Cells of Transition. This name is given to such cells 

 as are destined to undergo development into other forms of 

 tissue of a more or less permanent character. 1. Cells ob- 

 served in the development of the ovum of plants and animals. 

 2. Fibre cells. 3. Epithelial cells. 4. Cartilage cells. Such 

 cells are in the end to be transformed into various organs, 



