296
THE SEAS
'
for the rst few weeks of their existence and rise near the
‘
surface of the sea where they are carried in all directions
by tides and currents (Fig. 59).
At this stage they have
a pair of tiny shell valves between Which project a crown
'
'
,\
‘;_,;Drl
\.
a
.
/ /f
/ @ig:=w=mglm
'
.
Ï
": ' '. ' : "
-_-:-_.' =:_._
"
'w,‘:‘
:“
'
“5%“.
-'
.=Ë:Ï'Î-'.ÏiVäîä%%‘
}
»}.ÿ
_
‘°‘ëä'âËÿïï—*'
,
°
”"—"«enä'
Al
-
Ï:ËÎÏ
-
\' l
_
;-_=;‘
u—\\\\\\fg
'
_
sg.—Larval Stage of
greatly ehlarged.
»
_
of ne hai—rs by the rapid movement of which they
—' sWim
.
and collect their food.
At the end of their brief period
of freedom the little oysters, or such
them as have