18 DEEP SEA FISHES. 



have but two gills on each side, the first and the fourth arches bearing 

 none, though in these instances it is not entirely safe to infer much con- 

 cerning bathybial influences since what at first sight appears to have been 

 induced by abyssal conditions was actually in the inception near the sur- 

 fiice resultant from the acquisition of an illicium (bait and rod) with the 

 consequent sedentary habit. While nearly all of the deep sea Halieutoids 

 are two gilled, those dwelling near the surface are mostly two and one 

 half gilled, the reduction having proceeded thus far at least without aid 

 from deep sea conditions; yet there are some of the two gilled species that 

 approach the surface, for instance Dibranchus utlanticus Pet., or Malthopsis 

 sjKirsa sp. n., and these are more likely to represent the ancestors of the 

 deep sea sjiecies than to have been derived from the latter. 



Apparently the intestines have shortened with adaptation to life at great 

 depths, as if the species were farther removed from dependence on vegeta- 

 tion as food, through decrease in its consumption by the prey. This is 

 counterbalanced in many fishes by an increase in the size and distensibility 

 of the stomach. Unfortunately removal of the viscera, some time in the 

 early history of the .collection, from the larger specimens has taken away 

 a source of information concerning food and habits. 



It is too early yet to say in which diiection deep sea influences tend to 

 modify the habits of reproduction, whether toward the egg laj'ing or toward 

 the ovoviviparous ; it can only be said that many species lay eggs and many 

 others extrude living young. 



From conditions necessitating reduction in the amount of activity and 

 adoption of more sluggish habits the muscles of some bathybial fishes have 

 become excessively reduced, see Dolopichthi/s allector, Plate XIV., fig. 1. 

 Besides the general modifications undergone in the skeletons, many have 

 suffered great modifications in particular sections of the osseous structure 

 from lack of the uses to which they were adapted by ancestors ; a marked 

 illustration of this occurs in the neural spines of Caulolepis Avhich have so 

 declined as to lie nearly parallel with the vertebral column, Plate XII., fig. 1. 



Whether as much activity is possible in the midst of the great pressures 

 surrounding bathybial species as exists in the species near the surface, the 

 conditions of skeletons, muscles, fins, and gills indicate very plainly its non- 

 existence. It may be said that activity such as exists near the surface can- 

 not exist at great depths because of the diminished supply of oxygen, but, 



