200
J. H. S . BLAXTER AND F. 0. T. HOLLIDAY
(lS56) described the position and structure of the micropyle, penetrating
all three layers of the chorion in Clupea p a l h i i .
Few analyses have been made on the composition of the clupeid egg.
The peripheral cytoplasm in the egg of Clupea p a l h i i contains a
number of cortical alveoli with neutral muco-polysaccharide contents
(KanoX, 1953 ; Yamamoto, 1956); the same is true of the herring egg
(Holliday, unpublished). The alveoli contain no lipids ; the main yolk
particles are separate from these, and give only a weak response to the
P.A.S. test. Hempel (personal communication) found that the mean
fat content of herring eggs was 1.32% of the wet weight and probably
about 8.3% of the dry weight, in the southern North Sea in 1961.
Lasker (1962) analysed the egg of Surdimp caerulea and found that
over 70% of the dry weight was protein ; lipids constituted 13% of the
dry weight and the water content of the yolk averaged 91.2%.
B. Tolerance to external conditions
I n the body of the parent herring the gametes are maintained in a
relatively favourable environment. Herring eggs are slightly hypotonic to the body fluids of the female parent; Holliday (unpublished)
obtained freezing point values of -0.75"C for ripe eggs in the gonads of
female herring with blood freezing points of -0-92"C. Barnes (personal
communication) and Kolliday (unpublished) both obtained values of
-0.92"C for the sperm of herring, i.e. the malc gametes were isotonic
with the blood of the parents.
On Being rcloased into the water the gametes often sxperience a vast
change in concentration of the external medium. Htmmg ofitnotic forcen
are often exerted on thcm, and, with their Itirgf: H I J ~ ~ ~ W :
t i r w i / v o l t ~ r ~ ~ ~ ~
ratios, one might imagine them to be enpcaially HllSC~!JJtitJh t,o oomotio
death. On the contrary, they appear very tolerant (see Section 111, C).
It is difficult to determine just what mechanisms are employed by
the qmmatozoa to survive these osmotic forces. They could survive by
being impermeable or by being freely permeable, thereby changing
drastically in composition but avoiding any osmotic gradient ; alternatively there may be some non-electrolyte present which is capable
of setting up a force opposing the osmotic forces of the environment.
Much more has recently been found out about regulation in the egg,
and this is discussed in detail in a later section. When released into the
water, whether fertilized or not, the herring egg rapidly approacheu
isotonicity with the medium. The osmotic forces are t h w cqualizcd
passively. True regulation depends on the suhequcrit emhryonic
development (see Section 111, C).
J. H. S . BLAXTER AND F. 0. T. HOLLIDAY
(lS56) described the position and structure of the micropyle, penetrating
all three layers of the chorion in Clupea p a l h i i .
Few analyses have been made on the composition of the clupeid egg.
The peripheral cytoplasm in the egg of Clupea p a l h i i contains a
number of cortical alveoli with neutral muco-polysaccharide contents
(KanoX, 1953 ; Yamamoto, 1956); the same is true of the herring egg
(Holliday, unpublished). The alveoli contain no lipids ; the main yolk
particles are separate from these, and give only a weak response to the
P.A.S. test. Hempel (personal communication) found that the mean
fat content of herring eggs was 1.32% of the wet weight and probably
about 8.3% of the dry weight, in the southern North Sea in 1961.
Lasker (1962) analysed the egg of Surdimp caerulea and found that
over 70% of the dry weight was protein ; lipids constituted 13% of the
dry weight and the water content of the yolk averaged 91.2%.
B. Tolerance to external conditions
I n the body of the parent herring the gametes are maintained in a
relatively favourable environment. Herring eggs are slightly hypotonic to the body fluids of the female parent; Holliday (unpublished)
obtained freezing point values of -0.75"C for ripe eggs in the gonads of
female herring with blood freezing points of -0-92"C. Barnes (personal
communication) and Kolliday (unpublished) both obtained values of
-0.92"C for the sperm of herring, i.e. the malc gametes were isotonic
with the blood of the parents.
On Being rcloased into the water the gametes often sxperience a vast
change in concentration of the external medium. Htmmg ofitnotic forcen
are often exerted on thcm, and, with their Itirgf: H I J ~ ~ ~ W :
t i r w i / v o l t ~ r ~ ~ ~ ~
ratios, one might imagine them to be enpcaially HllSC~!JJtitJh t,o oomotio
death. On the contrary, they appear very tolerant (see Section 111, C).
It is difficult to determine just what mechanisms are employed by
the qmmatozoa to survive these osmotic forces. They could survive by
being impermeable or by being freely permeable, thereby changing
drastically in composition but avoiding any osmotic gradient ; alternatively there may be some non-electrolyte present which is capable
of setting up a force opposing the osmotic forces of the environment.
Much more has recently been found out about regulation in the egg,
and this is discussed in detail in a later section. When released into the
water, whether fertilized or not, the herring egg rapidly approacheu
isotonicity with the medium. The osmotic forces are t h w cqualizcd
passively. True regulation depends on the suhequcrit emhryonic
development (see Section 111, C).