GENERAL DISCUSSION. 19 
in the presence of freezing temperatures and intense pressure acting as 
conservators of organic tissue and preventing its disintegration, a supply 
of oxygen such as that existing in the surface waters is not at all neces- 
sary. The reduction of activity, from difficulty of movement in the nearly 
solid media under enormous pressure, from the extreme low temperature, 
and from the limited supply of oxygen, alike affects all the animals of the 
bathybial fauna, so that the equilibrium is practically unchanged and none 
of the species is either more or less at a disadvantage on account of the 
greater inertness. 
The distribution of species is discussed in the general remarks on the 
different groups and is indicated in the lists that pertain to them; the dis- 
tribution of genera is made a subject of special treatment below. 
