3o6 



C. U. Ariíins Kappers 



They do not form a bunch of light organs by reason of their basis, 

 the head, being round or the peripheral part of the rhabdoms being larger 

 than their central ending, but on account of their vaulted field of visión. 



We are still far from having found the solution of the structural cha- 

 racteristics in the optic nervous system, specially the eye itself. This 



Fig. 32. — Several rhabdoms of the Li- 



bella (Aeschna grandis) cut longitudi- 



nally and showing the fine light cañáis 



inside the rhabdoms. 





Fig. 33- — Several rhabdoms of the 



Libella (Aeschna grandis) cut transver- 



sally, showing the light cañáis in each 



rhabdom. 



problem will — no doubt — puzzle the mind of still many generations of 

 neurologists. So much however sees, to be sure that the solution will 

 be found in the way of the processes of taxis and tropism and that Santia- 

 go Ramón y Caja) will be always remembered as the first who indicated 

 this way. 



R 



c s u m c . 



It has been rightly emphasized by 5". Ramón y Cajal that tropistic 

 factors act the chief part in the arrangment of nerve elements. 



Although this is a process in which the whole metabolism of the cell 

 ¡s involved í:^ neurobiotaxis) the leading factor is stimulation or its mne- 

 mic representative, which may act chiefly by means of bio-electric forces. 



