REPORT ON THE DEEP-SEA FISHES. 323 



at the base near their junction with the olfactory lobes. The optic lobe is of the usual 

 size. On the lower surface on each side, between the bases of the Nervus Opticus 

 and Trigeminus, a special lobe, not found in ordinary fishes, is met with (m). 

 From this lobe a very stout nerve (g), which is thicker than any other cerebral nerve, 

 originates, and extending downwards and slightly backwards and outwards, divides into 

 two equally stout branches, which are bent abruptly on entering the orbital cavity and 

 which pass backwards. Ramifications of these nerves supply the two suborbital organs. 

 I name this nerve Nervus phosphorius, and the lobe from which it originates Lobus 

 phosphorius. Morphologically, this nerve is to be considered as a highly developed, 

 modified anterior branch of the Trigeminus, and it thus appears homologous with the 

 electric nerve of Torpedo. 



d. Function. 



The spicule-layer of these organs and their general structure establish their 

 phosphorescent nature with sufficient certainty. It is an extraordinary and remarkable 

 fact, that the light-reflecting spicule layer is found surrounding the immersed proximal 

 portions of these organs only, and does not extend so as to form a reflector also for 

 the superficial portion. It has been suggested by Dr. Giinther that the suborbital 

 organs can be projected partially, and that they then extend far beyond the surface of 

 the fish. There is no reason why this should not be possible ; but it has not been . 

 observed in any of the specimens at my disposal. The light, which is presumably '! 

 emitted from these organs, is thrown in such a direction, that it illuminates the field of 

 vision of the fish ; they thus enable the fish to see, and must be considered as aggressive 

 organs. 



e. Development. 



The structure and position of the organs indicate that they, like those described "^ 

 above, have been developed from a portion of the slime-canal system. 



CONCLUSION. 

 a. Comparison of the Different Phosphorescent Organs of Fishes. 



All the organs which have been described above, have, however difierent they may 

 be in other respects, one thing in common, namely, that 'either the whole of the organ or 

 part of it is glandular. In the latter case the glandular portion is always proximally 

 situated and other structures of a special nature are added to it, which are always found in 

 the distal part of the organ. "We may, therefore, assume that the original form of the phos- 



