29S Papers from the Marine Biological Laboratory at Tortugas. 



face of the water, when seen as their enemies see them. They are then 

 viewed at a different angle. They appear at times against the reef or bot- 

 tom, at times against the totally reflecting surface film, and at other times 

 against the blue translucence of the more distant water. I have been able to 

 assure myself of the conspicuousness of the fish under these circumstances by 

 two methods. ( i ) By the use of a reflecting water-glass,' I have succeeded, 

 without using a diver's suit, in seeing fish as they appear lo other fish. (2) 

 By means of a submerged camera (Reighard, 1908) I have photographed 

 them while they were engaged in their usual activities in their normal en- 

 vironment. Several of these photographs are reproduced in plates i to 5, 

 and are sufficiently described in the explanations of the plates. They show 

 certain of these fish as they appear to a submerged observer and seem to me 

 to afford a sufficient demonstration of their conspicuousness. (For further 

 evidence see the plates in Evermann and Marsh, 1902; Jordan and Ever- 

 mann, 1905; Jordan and Scale, 1906; and Saville-Kent, 1893.) 



Many of these fish are rendered still more conspicuous by their form and 

 movements. The great compression of the body (Chcctodon, plate 3 ; Poma- 

 canthus, Angclichtliys, Hepatus, plate 3, fig. 5; plate 5) exposes to view a 

 greater surface which may be further increased by the expansion of the 

 dorsal and anal fins. The movements of the same fish are peculiarly slow and 

 erratic and suggest those of a butterfly on the wing. This peculiarity arises 

 from the use of the pectoral fins rather than the caudal in ordinary progres- 

 sive movements. The caudal appears to be held in reserve for emergencies, 

 as when the fish are forced to flee to shelter. This erratic, jerky method of 

 locomotion by means of the pectorals is not confined to forms with com- 

 pressed bodies and expanded fins, but is found also in all the Labridae ob- 

 served (Thalcissoma, Iridic, Sparisoma, Scarus, et al.). 



^ This is a rectangular box of galvanized iron, 2 feet long and with ends 6 by 8 

 inches. In the interior of the box at each end is a mirror firmly fixed in a metallic set- 

 ting and placed at an angle of 45° with the long axis of the box. The reflecting faces 

 of the two mirrors are consequently parallel and they are directed toward each 

 other. One end is heavily weighted with lead, so that when placed in water the box 

 floats in an upright position with about 10 inches of the upper end projecting above 

 the surface. Opposite the lower mirror is an opening 6 by 8 inches filled with plate 

 glass bedded in aquarium cement. Opposite the upper mirror are 2 tubes soldered 

 to openings in the side of the box and so spaced that the observer may look through 

 them at the upper mirror. The tubes are lined with chamois skin and so constructed 

 that the objective ends of a pair of field glasses may be inserted into them and firmly 

 clamped in place. A handle on either side of the box enables it to be held steady. 

 The observer, while wading, holds the box in front of him with the lower end im- 

 mersed. He may then see objects beneath the surface reflected in the two mirrors, 

 just as they would appear to him if his head were beneath the surface. In using this 

 apparatus I finally dispensed with the field glasses, chiefly because I was able to get 

 so near the fish that their use was unnecessary, but partly because the double images 

 formed by the glass mirrors interfered somewhat with their use. The apparatus 

 would be more efiicient if double images were avoided by the use of metallic mirrors. 

 These could be kept from tarnishing by sealing the box hermetically by means of 

 glass plates cemented over the inner ends of the tubes for the eyes. With such an 

 apparatus field glasses could be used and, within the limits set by the opacity of the 

 water, the fish could be studied with them as birds are studied in air. 



