PIGMENTS ON THE LOWER SIDES OF FLAT FISHES. 



55 



the slate by an interval. The areas of contact were shown by dropping 

 the smaller flounder, in the moist fresh state, on a surface of dry slate, 

 when the areas in contact moistened the slate, while the part of the 

 slate not touched by the fish remained dry. 



Fig. 2 is a diagram of the impression thus produced on the slate by 

 the fish, and it will be seen that it is a remarkably exact negative of 

 the distribution of the pigment on the lower surface of the fish. The 

 projection of the area of contact towards the dorsal edge of the fish is 

 not so extensive as the unpigmented area on the dorsal region of the 

 body of the fish, and the tail is in contact with the slate. But in view 

 of the exact correspondence in other respects, these differences are 

 easily explained, and do not invalidate the evidence. The white patch 





Fig. 2:— Iiupressiou of under side of Flounder on dry slate. 



in Fig. 2, corresponding to the area of pigment on the lateral line, and 

 the remarkable correspondence of the area of contact ventrally with 

 the outline of the pigmented area in the fish, as shown in Fig. 2, are 

 sutliciently striking. With regard to the isolated patch of pigment 

 on the lateral line, a difficulty arises. Since this small area is an island 

 surrounded everywhere by surfaces in contact with the bottom, how 

 could light reach it ? 



In order to prove that light does reach the pigmented areas, I had 

 recourse to photographic action. The same flounder was placed, while 

 still alive, on a sheet of bromide printing-paper in the dark room, and 

 then exposed for a few seconds to daylight, to light coming horizontally. 

 The result of one such experiment is shown in Fig. 3. Here, again, 



