224 HOVEY JORDAN 



serving as an 'optic-reflex' transmission path is denied by 

 Nicholls, who adopts the theory, originally suggested by Dendy, 

 that the fiber automatically controls the flexure of the body. 



In support of this idea Nicholls has recentlj^ brought forward 

 some experimental evidence. He pierced the tails of a large 

 number of sharks and rays in the region of the sinus terminalis, 

 his purpose being to sever the posterior connections of Reissner's 

 fiber. This experiment usually caused the fish to assume an 

 abnormal attitude, in most cases an uptilting of the posterior end 

 of the body. Subsequent microscopic examination of the tails 

 of these fishes revealed the fact that the reaction occurred, in 

 general, only when Reissner's fiber had suffered considerable 

 recoil. 



I have recently repeated on the brook-trout these experiments, 

 and have performed several others of a slightly different nature. 

 The results do not seem to confirm for this teleost Nicholls' 

 theory, for, although a mutilation of the sinus terminalis region 

 does cause the reaction which he described, the same reaction 

 can also be induced by cutting the tail in several other regions 

 which, being outside the limits of the posterior end of the spinal 

 cord, leave the sinus terminalis, and hence Reissner's fiber, 

 intact. Whether this reaction is due to some purely mechanical 

 effect or is brought about through the agency of the nervous 

 system, I have not yet determined. There is some evidence to 

 show that the normal attitude of the body is reassumed as soon 

 as the tail has healed and regenerated. 



Operations aimed at cutting the fiber in the fourth ventricle 

 were carried out on the hamlet (Epinephelus striatus Bloch) at 

 Bermuda. The reactions of operated and of normal fishes to 

 all the various categories of stimuli applied were practically 

 identical. In view of the fact, however, that microscopic exami- 

 nation of the operated brains failed to establish conclusively the 

 success of the operation, it is not desirable to give much weight 

 to these experiments. They merely suggest that the fiber may 

 have no function so far as concerns the reactions of the fish to a 

 variety of stimuli. It was my intention to have repeated these 



