3 I2 



HISTOGENESIS 



porting tissue of the central nervous system ; the neuroblasts are primitive nerve 

 cells and by developing cell processes are converted into neurones. The neurones 

 are the structural units of the nervous tissue. 



Germinal Cells 



fy 



Ependymal Cells 



6 Indifferent Cells 



Mitotic Indifferent 

 Cells 



Neuroglia Cells 

 Neurobfasts 



FIG. 299. Diagrams showing the differentiation of the cells in the wall of the neural tube and the theo- 

 retical derivation of the ependymal cells, neuroglia cells and neuroblasts (after Schaper). 



FIG. 300. A , Transverse section through the spinal cord of a chick embryo of the third day showing 

 neuraxons developing from' neuroblasts of the neural tube F and from the bipolar ganglion cells, d. 

 (Cajal); B, Neuroblasts from the spinal cord of a seventy-two-hour chick. The three to the right show 

 neurofibrils; C, incremental cone. 



