Phenomena of neiirobiotaxis ¡n the optic systcm 



305 



occuring in all cases where onc opeiiiiig gives entrance to the light for all 

 the neuroepitheüum cells, viz. ¡t holds good for all monoapertiiral eyes 

 (See fig. 29). 



On the other hand and consistently with this theory, we find no hollow 

 eye in those cases, where no coimiwn entrance for the light to all neuroepi- 





fj""*^— **^' 



Fig. 30. — Section through the eye of Musca (Section made by Dr. L. Peeters.) 



thelium cells occurs, i. e. in such cases, where every neuroepithelium cell, 

 every rhabdom, is provided with its own light aperture, i. e. in the pliiri- 

 apci'tnral eye of insects (fig. 30). Here the neuroepithelium, in its for- 



Fig. 31. — Hcad with eyes of the Libella (Aeschna granáis). 



mation and direction follows also the direction of the rays in each 

 individual cell, but thesc, proceeding as a whole from the entirc surrounding 

 (the whole horizon), are not divergent and the light percepting cells are 

 arranged in a convex form on the head (somctimes covering the whole 

 head as is seen in the Libella) (fig. 31). 



Homenaje a Caja I ^o 



