FUNCTION (IF LATERAL-LINE ORGANS IN FISHES. 191 



had recovered from the operation, to test them in comparison with normal indi- 

 viduals by subjecting both to a particular stimulus. In this way I expected to 

 ascertain whether with the loss of the lateral-line organs the ability to respond to 

 certain stimuli would disappear. To eliminate the effects of the operation as far as 

 possible 1 usually tested a third series of tislies in which incisions had been made to 

 reach the nerves, but in which the nerves themselves had not been severed. 



In all the fishes, except the dog-fish and the skate, the nerves were cut by the 

 method described in my previous paper (Parker, 1903a, p. 59), i. e., the tislies were 

 etherized by being put for a few minutes in sea water containing a little ether, and 

 the fifth and seventh nerves were then cut by an incision behind the eye, and the 

 lateral-line nerve by an incision just behind the head; the few lateral-line organs 

 between these two incisions were then extripated. In the dog-fish and the skate the 

 operation was similar, except that the fifth and the seventh nerves were more con- 

 veniently cut from the roof of the mouth than from the exterior. 



The chief objection to this method of operating lies in the fact that in cutting 

 the root of the seventh nerve it is necessary also to cut that of the fifth, so that the 

 tactile sensibility of much of the head, as well as the innervation of the muscles of 

 the jaws, are almost always lost. Notwithstanding the apparent severity of the 

 operations the fishes usually recovered, and even a few hours after the operation 

 began feeding and acted in most respects normally. The majority lived for several 

 weeks, and some of them for over a month. Care was exercised, however, to see 

 that they were properly fed, for the paralyzed state of the muscles of the jaws. 

 though not interfering much with respiration, did make it difficult for the fish to 

 grasp food. 



Normal and, as I shall call them, cut fishes were then subjected to the following 

 range of stimuli and their reactions noted: Light, heat, salinity of water, food, oxy- 

 gen, carbon dioxide, foulness of water, pressure of water, currents, stimuli to equilib- 

 rium, vibrations of high frequency (sound), and vibrations of low frequency. 



EXPERIMENTS. 



Light. — To ascertain whether light was a stimulus for the lateral-line organs the 

 following device was used: An oblong glass aquarium, measuring about 60 cm. in 

 length, 25 cm. in breadth, and 25 cm. in height, was half-covered with opaque cloth, 

 so that one end and the adjacent halves of the top and of the sides were impervious 

 to light. The apparatus was set up in a dark room and illuminated by a 16-candle 

 incandescent electric light, so placed that the light fell across the uncovered half of 

 the aquarium, but without entering the darkened half. The aquarium was tilled with 

 sea water and specimens of Fundulus heteroclitus were introduced to see if they 

 would assemble in the light or in the dark. It was soon found that these fishes 

 followed one another by sight, and the records finally taken came from experiments 

 in which single fishes w r ere put in the aquarium and their reactions observed. After 

 a fish had become accustomed to its new surrounding, which happened usually in 

 about ten or fifteen minutes, and which was indicated by the fish leaving the bottom 

 of the aquarium and beginning to sport about near the surface of the water, obser- 

 vations were made at intervals of one minute as to whether the fish was in the dark 



