450 PROCEEDINGS OF THE AMERICAN ACADEMY. 



break the fibre. These individuals showed a marked difference in be- 

 havior from those in which the fibre had been broken. The former, 

 after recovery from shock, were apparently normal in their reactions. 

 Those in which the fibre had been broken showed a slowness in response 

 to optical stimuli. For example, such an animal, in swimming about 

 the tank in which it was confined, would bump into the sides of the cage. 

 If any obstacle were suddenly placed in front of it while swimming, its 

 effort to avoid the obstacle would come apparently too late to prevent 

 collision. Those individuals in which subsequent autopsy and examina- 

 tion showed the fibre to be intact exhibited much greater dexterity and 

 quickness in avoiding obstacles. The behavior of the animals operated 

 on was constantly compared with normal individuals kejjt with them in 

 the same enclosure. These experiments could be made entirely con- 

 clusive only by comparing the time reactions in cases where the fibre was 

 cut with those where it remained uncut. No attempt has yet been made 

 to do this. 



The apparatus which is the subject of this paper forms, I believe, a 

 short circuit between the visual organs and the musculature, and has for 

 its function the transmission of motor reflexes arising from optical 

 stimuli. This view as to its function is supported by many distinct 

 lines of evidence, which are here classified and summarized. 



(1) Anatomy. There is normally in all vertebrates a group of cells 

 lying in the optic lobes which by some of their processes are in direct 

 connection with the central terminations of the optic nerve, and by 

 others with the Purkinje cells of the cerebellum. Their axons pass by 

 the shortest route through the ventricles and canal to the posterior por- 

 tion of the nervous system, where they pass into the cord and probably 

 out through the ventral roots to the musculature. These anatomical 

 connections make it probable that this apparatus is a direct path for 

 the transmission of motor reflexes arising from optical stimuli. The 

 connection with the Purkinje cells of the cerebellum, it is equally evi- 

 dent, is for the coordination of muscular movements. 



(2) Experimental Physiology. When Reissner's fibre is cut or 

 broken, the animal loses the power of responding quickly to optical 

 stimuli. This is not due to the shock resulting from the operation, for 

 animals on which the equivalent operation has been performed without 

 breaking the fibre are nearly or quite normal in this respect. 



(3) Com-paralive Physiology, (a) In any one group, as for example 

 the teleosts, the apparatus has its highest development in those animals 

 which are most active. In the predatory and rapacious bluefish (Poma- 



