16 DEEP SEA FISHES. 



Most often the eyes of bathybial aiiinials are larger than those of their kin- 

 dred near the surface. Entire ab.sence of light would have favored the de- 

 terioration and lo.ss of the eye, but the eyes have become rudimentary in 

 hardly a dozen of the multitude of known deep sea species. The list of the 

 so-called blind forms of great depths includes Benthobutis Morenhji Ale, Ttjph- 

 lomis ncmis Glint., Aphi/onus gekdinosus Glint., Ajjhyowis mollis G. B., Bara- 

 thronus bicolor G. B., Ahxetcrion Parfaiti Vaill., Tau>-cdophidiuni Hextii Ale, 

 Sciadonus pcdlcellaris sp. n., Leucicorus lusciosus sp. n., Dysovima buccphalus Ale, 

 D//somvioj)\is mucipariis Ale, and Mijxine circifrons sp. n. Other species of 

 Myxine should be included in a complete list of mainne blind fishes, but the 

 lo.ss of the eyes in this genus is to be attributed to parasitic habits rather 

 than to bathybial conditions. Bentholjatis, a recently discovered Torpedo, is 

 the only blind Selachian known. Eight of the others on the list are Brotu- 

 loids, and two, Dysomma and Dysommopsis are Muroenoids. In all these 

 cases, Myxine being excepted, the eyes have become rudimentary and are 

 more or less inefficient as visual organs. The case of Leucicorus is peculiar 

 in that the blindness is comparatively recent, if indeed the loss of the eye 

 is not an old age character and subsequent in the individual to an ordinary 

 useful organ in the early stages. Nearly all of the species on the list, ex- 

 cepting only perhaps Sciadonus and Myxine, dwell in the ooze, and on all 

 of them compensation for tlie lo.ss of sight appears in an inordinately devel- 

 oped Lateral Canal System. On Sciadonus, Plate F, figure 4, in addition to 

 the increased prominence in the development of the system there are con- 

 .siderable sensory developments on the fins. This genus is more likely to 

 liave the habit of swimming freely at a distance from the bottom. Tiie 

 greatest amount of differentiation of the visual oigans known among bathy- 

 bial fishes occurs on Ipnops ; here the ocular structures cover the whole 

 top of the head and depart radically from the common definition of eyes, 

 but, as Mosely has shown, they still retain the function of sight. Appar- 

 ently they have the additional functions of flashlights and i-eflectors ; they 

 are to be seen on Plate H, figures 2 and 2a, as they appear on a fresh speci- 

 men. Two species of this extraordinary genus are now known, I. Murrayi 

 and /. Agasskii, the latter from the present collection. Commonly in the 

 modification of tlie eye the outer structures are the first to deteriorate, 

 while tlie ball remains and gradually becomes very minute, as in Aphyonus 

 and otliers, before final disappearance. Li Barathroims bicolur, however, the 

 ball has disappeared and the large orbit has undergone a modification which. 



