24 SUPEK-ORGANIC EVOLUTION 



project a distinct image in the expansion of the 

 optic nerve. 1 



The necessity of an explanation emboldens me 

 to state something which seems to throw light on 

 this interesting problem. I believe that the situa- 

 tion of the supra-oesophagic ganglion and its 

 proximity to the coloured spots have the same 

 origin, and that they respectively owe their situation 

 to a phenomenon of phototaxia. The animal 

 adapts itself according to the light, and the point 

 by which it most adapts itself is that which acquires 

 the most activity, the more so when the luminous 

 phenomena are always accompanied by chemical 

 caloric action, etc. Thus, the coloured spots and 

 the aforesaid ganglia retain a relation with each 

 other, because both are the product of the great 

 dynamic force in the point where adaptation has 

 commenced. We have still to explain why the 

 spots are regular and in couples, but this question 

 is one with the symmetry of bodies, and probably 

 the explanation of the one thing will come with that 

 of the other. 



With regard to the lenticular epidermic thicken- 

 ing, which is the point of departure of the evolution 

 of the crystal, Cajal implicitly replies by saying 

 that this lenticular thickening has a radius and an 



1 Kamon y Cajal, The Texture of Man's Nervous System and the 

 Vertebrates, p. 8. 



