_
SWIMMING ANIMALS
.
81
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very familiar to those accustomed to rambling along our
beaches.
They are the so—called ‘_‘ mermaids’ purses,” little
horny capsules with spines or .tendrils at the fOur corners.
..
The smaller, narrower type, with long curling tendrils at its
corners, is that of the dog-sh (Scyllz‘um), while the large,
broad ones with the four spines, belong to the skates
(Plate
The dog-sh eggs are attached to sea weeds by
the parents, who wind the tendrils Securely round the stem
of the weeds ; these eggs are occasionally to'be found on
weeds at low tide with the yolk and small developing sh
_
inside, because the " mermaid's purse
” ”is of course merely
_
the case in which the .egg lies. Thé skate’s eggS, on the
other hand, are deposited in deeper water, where they are
buried in the sand with the two spines projecting above the
surface, and through these a current of water is drawn into
the case by the developing sh for breathing purposes.
These eggs of the dog—shes and ska—tes take many months
to hatch, although most othershes batch out within about
‘
a fortnight after the eggs are laid.
_
One of the‘most surprising cases of spawning instinct is
"
exhibited by,a little sh that abounds on the shores of
'
California._ This sh, the Grunion (Lewesthes tenais),
-
belonging to the Atherine family, deposits its eggs in the
sandat the
along the sandy beaches.
This
‘
it does one to three
after the highest spring tid'e,
burying the eggs two or three inches beneath the surface
of the sand.
Here the eggs remain and develop, until in a
fortnight’s time, when the high tides once more cover them,
they are ready to hatch.
Now notice the providence of
nature.
If those eggs had not. been laid just after the
highest spring tide there is quite a possibility that the next
high spring tide a _fortnight later, might not have been quite ,
’
so high, thus preventing the eggs from being reached by the
‘
.
_
'
water ;
and in this case, being ready to batch, they could
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