MUCIFEEOUS CANALS OF FISH. 183 



mupiferous canal, Schultze has suggested * that it is a 

 sense-organ adapted to receive vibrations of the water 

 with wave-lengths too great to be perceived as ordinary 

 sounds. Beard also leans to this same view. However 

 this may be, it is remarkably developed io many deep- 

 sea fish. 



In some cases peculiar eye-like bodies are developed 

 in connection (though not exclusively so) with the 

 muciferons canal. Leuckart.f by whom they were 

 discovered, at fivst considered them to be accessory 

 eyes, but subsequent researches led him to modify 

 this opinion, and to regard them as luminous organs. 

 Ussow { has more recently maintained that they are 

 eyes, and Leydig considers them as organs which 

 approach very nearly to true eyes (" welche wirblichen 

 gehorganen sehr nahe stehen"). Whatever doubt there 

 may be whether they have any power of sight, there is 

 no longer any question but that they are luminous, 

 and they are especially developed in the iishes of the 

 deep sea. 



These are very peculiar. The abysses of the ocean 

 are quite still, and black darkness reigns. The 

 pressure of the water is also very great. 



Hence the deep seas have a peculiar fauna of their 

 own. Surface species corld not geneially bear the 

 enormous pressure, and do not descenl to any great 

 depth. The true deep-sea forms are, however, as yet 

 liltle known. They are but seldom seen, and when 



* "XJeber die Siiniesorf>;ane der Seitenliuie bei Fisohen und 

 Amphibien," Arch.fur Mic. Anat, 1870. 



t " XJeber muthmassllche Nebenaugeu bei einem Fische." Beriobt 

 fiber die 39 Vers., Veutscher Natiir/orscher, Giessen, 1864. 



X " Ueber den Bau der sog. aiigenalmlichen Fleckeu eiuiger 

 KnochenfiBche," Bidl. Soe. Imp. Moscow, 1879. 

 10 



