436 FEANCIS B. SUMNER 



opposite directions. The pupil of the eye is crescentic in form, 

 owing to a semicircular projection from the dorsal side of the iris. 

 This must largely eclipse the visual field overhead, though, as 

 will be pointed out presently, the fish can see in this direction, 

 even without any special movement of the eye. 



In most of these experiments, glass jars were used, whose bottom 

 areas were not large in comparison with the size of the fish.^^ 

 Except in special cases, the walls of these jars were left un- 

 painted. Since the fish commonly lay close to one or another side 

 of the jar, and its head was never more than a few centimeters 

 distant from one of the vertical walls, the animal's visual field 

 necessarily included much that lay outside of the jar alto- 

 gether. The different portions of this 'landscape' must have 

 varied greatly in their degree of illumination, from the bright 

 side toward the window, to the comparatively dark side viewed 

 in the opposite direction. That the fishes actually did, at times, 

 give attention to things seen through the walls of the jar, was evi- 

 dent from the fact that their eyes frequently followed my hand 

 or other moving objects held in their vicinity. It was likewise 

 found that the fishes could see objects directly overhead, since 

 they sometimes rose with great celerity to take food which was 

 dropped in from above, even in a larger tank with 25 or 30 cm. of 

 water, and certain more timid specimens became agitated when- 

 ever I moved objects directly over them, although at a consider- 

 able distance above the surface of the water. 



In the experiments thus far described, reference has been made 

 to the bottom alone. In some cases the fish itself covered a 

 fourth, or even more, of this bottom, w^hile another large part of 

 the animal's visual field was necessarily occupied by the vertical 

 walls of the jar, together with the lights and shades of the room 



*' Most of the rectangular jars used had bottom dimensions of 15 by 20 cm. 

 (These are the external measurements. In reality, the movable plates were some- 

 what smaller). Rectangular jars of a larger size were used, measuring 20 by 30 

 cm. at the bottom, the artificial patterns being 17 X 27 cm. The cylindrical jars 

 employed had a diameter of 20 cm., and a height of 12 cm. The fishes ranged in 

 length from 8.2 cm. to 19 cm. No. 1 had a length of 11.4 cm., no. 4 a length of 11.2 

 cm., no. 11 a length of 8.9 cm. 



