114 BIOLOGICAL LECTURES. 



of heat rays, thrown upon the leg of a frog whose brain had 

 been laid bare and covered with extract of beef caused it to 

 respond each time with reflex movements. 



Amblyopsis seeks the dark, regardless of the direction of 

 the light. An aquarium about eight feet long was placed in 

 the open, with the darkened end toward the north. The fishes 

 remained in the dark area all day, coming out at night. A 

 smaller aquarium was divided into two compartments, at first 

 with but a small connecting opening ; later with a double 

 partition, with an opening at one end of one partition and 

 another opening at the opposite end of the second partition. 

 One compartment and the connecting tunnel were dark. At 

 first there was a constant change of individuals from the dark 

 to the light chamber, but after several days they remained in 

 the dark chamber during the day. These experiments were 

 conducted in my laboratory where usually only diffuse daylight 

 prevailed. Jarring the aquarium or changing the water was 

 usually sufficient to cause them to come out into the lighted 

 compartment. It may be stated that the fishes found no diffi- 

 culty in finding the opening connecting the compartments, and 

 that the fishes in the dark were continually swimming past the 

 opening without attempting to come out. Rarely one passed 

 out into the light chamber, and then invariably showed signs 

 of uneasiness, frequently turning sharply and reentering the 

 dark chamber. 



Four blind-fishes which had been kept for a day in a vessel 

 painted black, and covered to exclude the light, were experi- 

 mented upon as follows : a ray of light from a mirror about two 

 inches in diameter was thrown on each successively. After 

 from one to five seconds the fishes became uneasy, the uneasi- 

 ness giving place to discomfort, finally resulting in vigorous 

 effort to get out of the way. 



Another jar, not painted, containing both blind-fishes and 

 blind Cambarus, was placed where light could be reflected upon 

 them from the mirror of a microscope. The Cambarus, if in 

 motion, came suddenly to a halt ; if quiet, backed or moved off 

 at once. The fishes also responded to the reflected light, but 

 it took several times as long for them to do so. 



