192 BULLETIN OF THE BTJKEAU < >F FISHERIES. 



or in the light. It soon appeared that a number <>f individuals were almost indiffer- 

 ent to the light, being found as commonly in one place as in the other. Others were 

 more generally in the light, and fishes were tested until fifteen such were obtained. 

 These fifteen were tested accurately by being placed individually in the aquarium 

 and by having their positions determined at minute intervals for ten minutes. In 

 150 observations these fishes were 93 times (62 per cent) in the light. 



They were then all operated upon by having the nerves to the lateral-line 

 organs cut. Twelve recovered and were tested as in the first experiment. In 120 

 observations these fishes were 7'.' times (tit; per cent) in the light. It is therefore 

 highly improbable that the slight tendency to assemble in the light shown by 

 some individuals of this species is in anyway dependent upon the lateral-line 

 organs; in other words, light is not a stimulus for these organs. 



Unit. — The stimulation of the lateral line organs by heat was tested also on 

 Fundulus heteroclitus. Five individuals with the nerves to the lateral-line organs 

 cut were compared with five normal individuals by subjecting them to water of 

 different temperatures in cylindrical glass jars 3.") cm. high and 23 cm. in diameter. 



The temperature of the outside water in which the fishes had been caught was at 

 this time of year (August) about L9.5 t'. When the five normal fishes were put in 

 the glass jar tilled with water at this temperature, they at once swam to the bottom, 

 and. as is usual with them when first introduced into an aquarium, remained swim- 

 ming about in the deeper water for some time. Finally, they rose to the surface 

 and sported about in the upper water, remaining there unless frightened by some 

 movement or other disturbance about them, whereupon they would again make a 

 temporary descent, tut fish acted in all respects like normal ones except, perhaps, 

 that they were not so agile in their movements, but this slight reduction in their 

 quickness of response was not d\w to the cutting of the nerves of the latteral-line 

 system, for it was observable in fish in which the skin, but not the nerves, had been 



cut. 



In water at 1-t ('.. the reaction-- of normal and of cut fishes were indistinguish- 

 able from those in water at L9.5 ('. 



At it ('.. much the same was observed asat 14 ('.. but there wasa slight though 

 noticeably greater tendency here to keep in the deeper water than at 19.5 C. This 

 tendency, however, was not pronounced enough to allow one to say that the fish had 

 deserted the top: after having been frightened away from the top they returned 

 less freely than at 1-t C. or 19.5 C. In this respect, however, the normal'and cut 

 lishes agreed. 



Two temperatures higher than 19.5 C. were tried. At 25.5 ( '. both normal 

 and cut lishes swam down, and for the most part stayed in the deeper water. Now 

 and then an individual would swim to the top, but it almost always quickly returned 

 to the bottom. In these respects normal and cut lishes were indistinguishable. 



At 30. 5 C C., both normal and cut fishes swam to the bottom of the vessel and 

 stayed there persistently. In the course of fifteen minutes not a single fish came to 

 the surface, whereas at 19.5 ('. all lishes returned to the surface usually in three to 

 four minutes. Moreover, the fishes continually nosed about on the bottom of the jar 

 as though they were seeking still deeper water. 



