XXVI TEGUMENTARY SYSTEM. 



may be emitted. In the second form it is evident that this organ could not 

 be employed for vision, being simply glandular, and possibly used to give 

 light, acting as a sort of lantern, the function being probably under the 

 control of the will. 



Professor Bernhardt, in 1853, observed on the Astronethes fieldii, Val. 

 common in the Atlantic Ocean, between 23 deg. and 6 deg. N. latitude 

 - — a fish .which possess lenses in these organs. It was only after sunset 

 that he discovered this fish in a drag-net. It is solely at that time 

 that the surface of the ocean begins to be ■ crowded by vast swarms 

 of Pteropoda and numerous Crustacea, .and possibly the . fish searches 

 for food among them, following them into greater depths during the day- 

 time. " In two instances I was so fortunate as .to catch the fish alive, when 

 I saw that it sent forth two strong and vivid greenish lights, which inter- 

 mitted momentarily and ceased altogether when the fish died. As 'the two 

 individuals only lived a few minutes after being taken out of the net, and as 

 the luminous appearance only showed itself distinctly in the dark,- it was not 

 until I procured a second specimen, a number of days after the first was 

 obtained, that I ascertained with certainty, that the light radiated from a 

 spot in the forehead, a little before the eyes, starting, as it were, from thence 

 along the back as far as the first dorsal fin : all the rest of the body remained 

 perfectly dark. On examining the whitish speck in the specimen preserved 

 in spirits, from whence the light radiated, a cellular tissue is found underneath, 

 •or rather within the skin, consisting of longish cells or meshes, filled with 

 an apparently fatty substance. No doubt this is the source of the phosphoric 

 light, although I have not been able to trace the substance, at least. not in 

 an aggregate form; beyond the eyes, so as to account for the extent back- 

 wards of the phosphorescence." 



There is likewise connected with the question of sight in fishes the subject 

 of the luminosity of other animals residing at great depths, and affording 

 what is known as abyssal light. Along our coasts luminosity of the surface 

 of the sea may be seen during our warm autumn months, among the exhibitors 

 of which are numerous small jelly-like animals more especially the Noctiluca. 

 In the account of the voyage of the " Porcupine," Thompson states, that 

 towards the north of Ireland in some places nearly everything brought up 

 seemed to emit light, and the mud itself was full of luminous sparks (p. 98). 

 Star-fishes and the larger invertebrates all exhibited this marvellous property 

 in the Faroes (p. 148). Nordenskiold found during the polar nights in 

 Spitsbergen in the snow-sledge a number of almost microscopic Crustacea 

 giving evidence of their existence by an intense bluish- white, light which 

 was emitted as soon as the sledge was touched, causing at every step a 

 bluish-white flame to burst forth. • . 



Few or none who have made voyages to the -tropics but must have been 



