310
THE BIOLOGY OF FISHES
its growth on other and higher forms of life. The c0m—
,
pound or bacteria, as it might be, is in some way connected
_
with the waste products of the latter, and it is signicant that
'
'whilst the coastal waters, with their proximity to the drain—
:
age from the rivers, are rich in plankton, the open ocean by
'
comparison appears
to be a desert.
We see again how
closely the many varied forms of life are linked together.
The plankton algæ are eaten by the larval shes and the
_
Î ; -
young stages of the innumerable forms of Invertebrates,
Gastropods, Bivalves, etc., that swarm in the water during
'
the spring and summer.
It is also believed that they
ï
constitute the principal diet of the planktonic Crustacea,
,
Copepods, Mysis, and the like, and various observers have
.
recorded their occurrence in the digestive tract of these
;;
forms._ But a doubt on the matter has been raised by
Pütter (1924) just with regard to the Copepods, and it may
a
be useful to note his arguments.
In the rst place, he is very sceptical with regard to
_
the previous records of Diatoms occ‘urrirîg in the stomachs
of Copepods, but a knowledge of the literature on this
É
particular subject is not a strong point with him. -Apart
from the earlier records one may. refer him to the recent
work of S. Marshall (1924) on* the food of the common
Copepod, Calanus nmarehicus, which was found to be
living mainly on -Diatoms in the summer and Radiolarias
È_'
in the winter. However, he indicates
and Diatoms do not occur in
at
the sametime; :…thus in
_
the Diatoms
th€if: maXima long before“ the Copepods,
_
and-out
open- 863 the {Dia—tomsfare near the surface '
whi1st
layer— Again;
he
whether the CopépbdS; are furnished
the
necessary acids
and in one form
(Haloptilus) he
that the stomach is short…ad »
to grow andinèrease
its volumeby
times. Even if th€—-Copepods do eat
the
only
;per cent. of; their
requirements, according to
.
.