DEEP-SEA FISHES. 301 



size than in their representatives at the surface. In such 

 fishes the eyes increase in size with the depth inhabited by 

 them, down to the depth of 200 fathoms, the large eyes being- 

 necessary to collect as many rays of light as possible. Beyond 

 that depth small-eyed fishes as well as large-eyed occur, the 

 former having their want of vision compensated for by tenta- 

 cular organs of touch, whilst the latter have no such accessory 

 organs, and evidently see only by the aid of phosphorescence. 

 In the greatest depths blind fishes occur with rudimentary 

 eyes and without special organs of touch. 



Many fishes of the deep sea are provided with more or less 

 numerous, round, shining, mother-of-pearl-coloured bodies, im- 

 bedded in the skin. These so-called phosphorescent or lumi- 

 nous organs are either larger bodies of an oval or irregularly 

 elliptical shape placed on the head, in the vicinity of the eye, 

 or smaller round globular bodies arranged symmetrically in 

 series along the side of the body and tail, especially near the 

 abdominal profile, less frequently along the back. The former 

 have not yet been anatomically examined. The number of 

 pairs of the latter is in direct relation to that of the segments 

 of the vertebral column, the muscular system, etc. (meta- 

 meres) ; and two kinds may be distinguished differing from 

 each other in their anatomical structure. The organs of one kind 

 consist of an anterior, biconvex, lens-like body, which is trans- 

 parent during life, simple or composed of rods {Chauliodus) ; 

 and of a posterior chamber which is filled with a transparent 

 fluid, and coated with a dark membrane composed of hexa- 

 gonal cells, or of rods arranged as in a retina. This structure 

 is found in Astroncsthcs, Stomias, Chauliodus, etc. In the other 

 kind the organ shows throughout a simply glandular structure, 

 but apparently without an efferent duct [Gonostoma, Scopelus, 

 Maurolicus, Argyropelecus). Branches of the spinal nerves 

 run to each organ, and are distributed over the retina-like 

 membrane or the glandular follicles. The former kind of 



