272
J. H. 8 . BLAXTER AND F. Q. T. HOLLIDAY
very low (<6%,) salinities. The increased water content of eggs
developing in these low salinities is reflected by the increase in size of
the egg (Holliday and Blaxter, 1961). This is also found in Clupea
p a l h i i (Galkina, 1957). Probably the mechanical pressure exerted by
the chorion limits water inflow ; this is certainly the case in the eggs of
Surdimps caerulea (Laaker and Theilacker, 1962a). There is inflow of
water into both the perivitelline space and the embryo. The chorion
appears to be freely permeable, although there may be a binding of
some ions by the colloid in the perivitelline space. Galkina (1957)
found that the chorion in Clupea pallasii waa strongest in salinities
1O-28%, .
Unpublished work by the authors and Hempel showed that, during
the early stages of development, the herring egg had little capacity to
regulate the osmotic concentration of the yolk, although the individual
cells of the blastula were apparently regulating. It was only after
gastrulation was completed that the whole egg was regulated to an
osmotic concentration equivalent to about one-third of the external
mcdiuni in salinities above 12%,, and, in lower salinities to a value
equivalent to 12%, (4=0.72). At this stage the whole of the exposed
surface of the yolk was enclosed within the endo- and ectodermal
layers. It seems probable that the ability to regulate is a property of
these cells. Lasker and Theilacker (1962s) showed that the degree of
regulation maintained by embryos of Sardimps caerulea was similar to
that in the herring (to about one-third of the external medium).
D. Effect of temperature, pressure and CO, on eggs*
The effect of temperature on the incubation time for clupeid eggu is
discussed in Section 111, B. Meyer (187%) fwind that normal tfcwlop.
ment took place from 22Oto l”C, but death occurred at - O.R‘”f!. ‘I’cmrn
(1958) found that eggs of Baltic herring would hatch at temperatures
as high as 18.5OC and Blaxter (1956) that the optimum temperatare
varied in different races.
Ewart (1886) found that eggs lowered to a depth of ahout 200 rn
(21 atm) and left for some days hatched normally in the s q u ~ r i u m after
being brought to the surface.
Kelley (1946) studied the effcct of carbon dioxide tension on the
eggs of Clupea p a l h i i and found that they could tolcratc pH valucs
ranging from 5.12-9.00 (the average ranging from 6.68-8.68), low pR
values retarding development. The eggs would tolerate CO, values
ranging from 0.00-67.76 ppm, the average values ranging from 0.08827.06 ppm.
Polikarpov and Ivanov (Voproay Ikhliol. 1, 683-9, 1961) found that exposure to
radiation (2 x 10-0 curies/litre) from @OSr and *OY led to abnormalities In developing
Ewaulis.
J. H. 8 . BLAXTER AND F. Q. T. HOLLIDAY
very low (<6%,) salinities. The increased water content of eggs
developing in these low salinities is reflected by the increase in size of
the egg (Holliday and Blaxter, 1961). This is also found in Clupea
p a l h i i (Galkina, 1957). Probably the mechanical pressure exerted by
the chorion limits water inflow ; this is certainly the case in the eggs of
Surdimps caerulea (Laaker and Theilacker, 1962a). There is inflow of
water into both the perivitelline space and the embryo. The chorion
appears to be freely permeable, although there may be a binding of
some ions by the colloid in the perivitelline space. Galkina (1957)
found that the chorion in Clupea pallasii waa strongest in salinities
1O-28%, .
Unpublished work by the authors and Hempel showed that, during
the early stages of development, the herring egg had little capacity to
regulate the osmotic concentration of the yolk, although the individual
cells of the blastula were apparently regulating. It was only after
gastrulation was completed that the whole egg was regulated to an
osmotic concentration equivalent to about one-third of the external
mcdiuni in salinities above 12%,, and, in lower salinities to a value
equivalent to 12%, (4=0.72). At this stage the whole of the exposed
surface of the yolk was enclosed within the endo- and ectodermal
layers. It seems probable that the ability to regulate is a property of
these cells. Lasker and Theilacker (1962s) showed that the degree of
regulation maintained by embryos of Sardimps caerulea was similar to
that in the herring (to about one-third of the external medium).
D. Effect of temperature, pressure and CO, on eggs*
The effect of temperature on the incubation time for clupeid eggu is
discussed in Section 111, B. Meyer (187%) fwind that normal tfcwlop.
ment took place from 22Oto l”C, but death occurred at - O.R‘”f!. ‘I’cmrn
(1958) found that eggs of Baltic herring would hatch at temperatures
as high as 18.5OC and Blaxter (1956) that the optimum temperatare
varied in different races.
Ewart (1886) found that eggs lowered to a depth of ahout 200 rn
(21 atm) and left for some days hatched normally in the s q u ~ r i u m after
being brought to the surface.
Kelley (1946) studied the effcct of carbon dioxide tension on the
eggs of Clupea p a l h i i and found that they could tolcratc pH valucs
ranging from 5.12-9.00 (the average ranging from 6.68-8.68), low pR
values retarding development. The eggs would tolerate CO, values
ranging from 0.00-67.76 ppm, the average values ranging from 0.08827.06 ppm.
Polikarpov and Ivanov (Voproay Ikhliol. 1, 683-9, 1961) found that exposure to
radiation (2 x 10-0 curies/litre) from @OSr and *OY led to abnormalities In developing
Ewaulis.