ANIMAL LIFE IN THE SEA 179 
is that in the daytime it lives at about 300 fathoms, 
but at night it rises to within 80 fathoms of the surface. 
Its young are crystal clear, and are surface forms living 
in the upper 80 fathoms. On the other hand, some 
members of the genus Alepocephalus live as far down 
as 1,100 fathoms, and have no light organs. Their 
young are the same black colour as the parents, and 
live also in the great depths. 
To sum up, so far as we know at present, forms 
which live in the surface waters of the ocean are crystal 
clear or pale violet or blue. Those which live in layers 
where only blue and violet rays penetrate freely tend 
to be silvery and to have large eyes and large light 
organs. Still deeper, where no red and no green rays, 
even in some instances no rays at all, penetrate, the 
colour becomes red or black, and light organs are small 
or disappear. That there is an intimate relation between 
the characters and colouring of the organism and the 
amount of light present is shown by the fact that when 
the larva inhabits the same depth as the parent it has 
the same colours. When it inhabits another zone it 
takes on the normal colouring of the inhabitants of 
that zone. Further, the fact that the forms from 
deeper water occur in different layers of water in 
different latitudes—the level corresponding to the 
degree of penetration of light in the particular latitude, 
so that the animals live higher up in high latitudes 
than in low—suggests that the life of the animals is 
strongly influenced by the amount of light present. 
One other point is interesting in regard to the life 
of these depths. Just as the littoral fishes often send 
pelagic larvae out to the open sea, so some of the 
abyssal fishes seem to have bathypelagic larvae, i.e. 
larvae living in the open water, but at considerable 
M 2 
