FRESHWATER FAUNA. 61 
has far less lime than Glodigerina ooze as it contains siliceous 
radiolarians and numerous pteropod shells. The abysmal 
region is peopled by a fair number of species scattered 
throughout the same phyla as are found in the neritic zone. 
Indeed there is every indication that the deep-sea has been 
gradually peopled from the neritic region by immigrants. 
All the animals show more or less striking modifications. 
All are carnivorous and many are phosphorescent. There 
are numerous Crustacea which often attain enormous size. 
Many of the large species are blind and of a light carmine 
colour. The fishes, as at present known, are few in species, 
all bony fishes or Ze/eostez, and of extraordinary appearance. 
(2) FRESHWATER Fauna.—The freshwater fauna is very 
diverse, as it includes dwellers in lakes, ponds, tivers and 
streams. It shows clear indications of having been derived 
from the Neritic zone of the marine fauna, though doubtless 
in some cases terrestrial animals have reverted to the 
freshwater. 
The same divisions, into swimmers or Nekton, Plankton 
and Benthos, can be made out, but the Plankton are very 
few in number, including Protozoa and a few freshwater 
Medusze. Amongst the swimmers we can notice two very 
primitive orders of fishes, the Gazofdei and Dignoi, which 
are confined to freshwater, apparently driven from the sea 
by more specialised types. 
Two important points should be noted. Firstly, a great 
number of freshwater forms can meet the physical vicissi- 
tudes of their habitat by encapsuling themselves and 
remaining dormant for some time (¢.g., Ameba, Infusoria, 
Rotifera, and Tardigrada). Secondly, the eggs and larve are 
hardly ever of the floating or free-swimming types, and are 
commonly protected by a hard capsule. As the rivers have 
been the lines of migration, the eggs and larve would, if 
floating, be borne back to the sea. 
The primitive freshwater types are especially interesting 
as leading along the path towards the terrestrial fauna. 
2. Terrestrial Fauna.—The terrestrial fauna has evi- 
dently been derived in the past from the aquatic. Only a few 
phyla appear tu have effected this migration. Of these the 
