FEEDING OF MARINE ANIMALS
199
rej ecting the large ones which accumulate Just within
-
the shell until the animal closes its shell quickly when they
are shot out, and only allowing the smallest ones to enter the
'
mouth and pass into the stomach.
The sea squirts feed m a somewhat similar manner, water
being drawn in at the one opening and rejected by the‘other
after having been sieved through a delicate lattice Work.
So ne is this lattice that, in a medium—sized seà'squirt,
it has been estimated thatthere are almost 200,000 openings
and about double that number of rows of cilia, the heating
of which creates the current.
Here again the food particles
,
.
'
_
l,
*.
‘\\
_
;
'
:
'
E
.
_
‘T'
à »
‘
'
42.—'—Oikopleura in “ house."
E., opening through which animal escapes from
_
house ; F., ne mesh guarding opening through which water is drawn ; H._, head en_d
-
of animal ; O., Opening through which water is expelled; S., sieve … which food xs
collected; T., tail of animal. Arrows show direction of water currentsin house (x 5)—
are 'entangled in a sticky substance and carried to the
mouth by special tracts of ciliaf. ' Near‘ relatives to the
_
sessile sea squirts are
tiny oating Appendicularians,
,
Which form part of the plankton. They feed in a most
amazing manner. - They do not catch the food directly
but form an elaborate gelatinous
“
house ”
much larger than “themselves, within which they live.
This “ house” is really a complicated apparatus for straining
sea =water»and is illustrated-inFigure 42.
ASa result of the
.