294 C. U. Ariens Kappers 



Consequently the drawing together of temporal fibers with nasal 

 fibers, from the other side, must be such that it shows at the same time 

 the influcnce of the cooperation of both temporal halves of the retina. 



This can only be effected by ^ partial decussation of the temporal re- 

 tinal fibers, not by a partial decussation of the nasal ones. A semidecus- 

 sation of the latter might indeed result from a cooperation of nasal and 

 temporal retinae in case of lateral visión but it could never result from the 

 (most importantj visión o f frontal objects, i. e. from bitemporal visión. 



This deduction equally explains, why the maximal number of homo- 

 lateral filíers is not identical with the entire temporal half of the retina, 

 but, only with the half of that half, i. e., about 25 percent of all optic- 

 fibers, since the other half of the temporal fibers must decussate as a re- 

 sult from its cooperation with the other side in bitemporal visión. 



As the macula is lying in the lateral field of the eye (in man about 

 4 m. m. sideways of the entrance of the optic nerve) it belongs essen- 

 tially to the temporal retinal half. 



W^ith regard . to the above deduction, it is interesting to note that 

 also the macula of every eye may have decussating and non decussating 

 fibers, which is likewise the cause of the fact that each macula is repre- 

 sented on both hemispheres, as also follows from the above m^entioned 

 neurobiotactic deduction. 



Some remarks on the neurobiotactic formation of the eye itself. 



From the large number of attempts to derive the eye of higher ani- 

 máis from that of lower ones, we may safely conclude that as yet no so- 

 lution has been found contenting all. The theories proclaiming our eye 

 to descend either from that of 7'unicates (Balfour and yelgt'rsma), of 

 worms (von Kennel), of from the spinal eyes of Amphioxus (Boveri) only 

 shift the point of interrogation, instead of giving a causal explanation. 



On the other side, the great analogy between the eye of ink-fishes, 

 and that of vertebrates, two so widely diflerent groups, show that the 

 same influences, working on quite different and not related objects, may 

 produce analogous results and as socalled convergent phenomena, make 

 US the more inclined to look for a causal explanation af this problem. 

 If anywhere it is here that we must first of all look at tropistic influen- 



