A VERS, Origin and Grozvth of Brain Cells. 213 



the connecting bands, as in those cases where the nerve cells 

 become completely separated. Ultimately of course the lym- 

 phatic spaces divide also by completing the capsular wall close 

 about each cell. 



The Division of the Cell. 

 Incisions of two very different kinds are found in the 

 bodies of the electro-motor cells. Those produced by cell 

 fission and those produced by unequal growth in response to 

 local pressure upon some part of the cell by blood-vessels or 

 nerve fibers from some neighboring cell. 



Relation to Blood-vessels. 



The large ganglion cells of the Torpedo brain have appar- 

 ently approached the limit of the size of nerve cells, which 

 require, as we know, specially good facilities for nutrition 

 (respiration and excretion included). The usual vertebrate 

 brain is made up of cells varying in size from .002 m.m, to 

 .1 m.m. and they are disposed about the courses of the 

 blood-vessels in such a way as to admit of easy transfer of 

 food to the cells and of the nitrogenous waste products away 

 from the cells. 



In the Torpedo's electric lobes, however, there is added to 

 the usual arrangements a special feature in the relation of the 

 cells to the blood-vessels. It consists in the migration of the 

 over-grown ganglion cells to the walls of the arterial capillaries 

 on the surfaces of which they spread themselves out and more 

 or less completely surround the vascular tubes so as to present 

 the appearance of being more or less deeply grooved or even 

 perforated. The cell wall in immediate contact with the capil- 

 lary cells is very thin and thus the very best facilities are pre- 

 sented for the performance of the physiological activities of the 

 brain cells. 



One of the anatomical causes of the increase in size of the 

 electric lobe of the Torpedo is the production of new cells 

 by the division of already functional electro-motor cells. 

 This division occurs most abundantly at the ventricular sur- 

 face of the lobe. 



