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- 
face 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 atlanticus Pet., or Malthopsis 
sparsa sp. n., and these are more likely to represent the ancestors of the 
deep sea species 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 direction deep sea influences tend to 
modify the habits of reproduction, whether toward the egg laying 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 Dolopichthys 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 which 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, 
