Fish, The Nerve Cell as a Unit. 



\Q% 



twice as long to produce certain results with a weak current as 

 when one of twice the strength was used. 



We must avoid the danger of regarding the cerebro-spinal 

 axis as a rigid and unyielding mass of substance. The action 

 of the brain is molar as well as molecular, as evidenced by its 

 general movements due to inspiration and expiration. In the 

 earlier stages of development there are migratory movements of 

 the neuroblasts of an amoeboid nature in order that they may 

 reach their destined positions in the adult structure. The so- 



Fig.^. After Cajal, showing the changes undergone by the cerebellar 

 granule cells, reading from left to right. 



called bipolar spinal ganglion cells are the permanent condition 

 in such low forms as the "fishes;" those of higher forms pass 

 from this stage in early development to the unipolar condition of 

 the adult. 



Fig. G. 



Fig. 6. After Fish (Central Nervous System of Desmognathus fusca), show- 

 ing the changes in the form of the neurocytes as they pass from the ental to the 

 ectal boundary of the layer of nerve cells. 



Cajal has shown that during their growth the granule cells 

 of the cerebellum pass through even more elaborate changes 

 than those of the spinal ganglia. Changes in the form of the 

 cells and their appendages are also apparent in the central ner- 



