PRODUCTION OF LIGHT 431 



of radial tubes or chambers containing gland-cells there are long 

 single cells radiating from the wall of the spherical sac to its 

 centre; these seem to be the light-producing cells, and it is 

 possible that the vertical rods in Ipnops are of similar nature. 

 On the other hand, the vertical columns of the organs of Ipnops 

 present rather more resemblance to the columns of the electric 

 organs of Torpedo than to any structures in luminous organs, 

 and it seems possible that they are really electric organs formed 

 by the modification of the muscular tissue of the orbits and 

 anterior region of the head ; but the columns are not described 

 as consisting of superimposed plates like those of electric organs. 

 Without further investigation nothing more can be said, and as 

 the capture of specimens of Ipnops from the abysses of the 

 ocean is a rare event we may have to wait a long time for any 

 addition to our knowledge on the subject. 



3. The phosphorescent or radiating organs of Halosauropsis, 

 as described by von Lendenfeld (Fig. 30, D.), are nothing but the 

 epithelial sense-organs of the lateral line and sensory tubes on 

 the head. They consist of slender columnar cells placed verti- 

 cally to the supporting membrane, and the organs have a free 

 surface to the cavity of the canal ; there is nothing in them re- 

 sembling in any way the structure of luminous organs. Whether 

 any of the accessory structures of the canals have a light-pro- 

 ducing function it is impossible to decide ; there is a peculiar 

 tissue beneath the scales of the lateral line which contains 

 numerous lens-shaped structures, and there are gland tubes 

 around the canal, but of the function of these structures we 

 have no evidence. 



Phosphorescence is a property of numerous Invertebrates, 

 and luminous organs as definite as those of fishes occur also in 

 some of them, for example in certain Crustacea, but no animals 

 except fishes are known to possess organs whose special func- 

 tion is to produce electricity. In certain fishes alone in the 

 animal kingdom does the energy produced by vital processes 

 assume the electrical form. 



The electric powers of the Torpedo are generally known ; 

 the commonest species is T. hebetans, also called T. nobiliana, 

 which is frequently taken on the south coast of England and 

 occasionally on the other coasts of Great Britain and Ireland. 

 This species and others of the same genus occur more abund- 



