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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. 



EpendymalCells 



Germinal Cells 



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. 



