110
THE BIOLOGY OF EUPHAUSIIDS
only the right side was developed and another one in which both sides
had produced spermatophores. I n E. krohnii, he finds that both the
left and right series of testicular vesicIes develop but that the right vas
deferens is very much reduced with hardly any lumen. The right
spermatophore sac is present but is also reduced and is only capable of
producing very small spermatophores which contain only a few spermatozoa. No comparable assymetry of the male copulatory organs was
present.
They are
spherical in shape, and in Meganyctiphanes norvegica have a diameter
of 9 p when they are released from the testicular vesicles but by the
time they reach the spermatophore sac their diameter has increased to
about 1411.. Most of them are still spherical but from here onwards
they are compressed into various shapes because they become packed
in the spermatophore which is being formed.
There is no detailed information on how the male uses the petasmae
to transfer spermatophores to the female. The shapes of the male
petasmae and female thelyca are peculiar to each species but how these
peculiarities function in the act of mating is unknown.
Mating of M . norvegica usually takes place in February in the Clyde
and nearly every female has spermatozoa present in the thelycum by
the end of February (Fig. 41) although the eggs are not usually laid
until the beginning of April. On the other hand, spermatophores are
formed by male Thysuno&sa raschii in the Clyde at the same time,
February, as by Meganyctiphanes norvegica but mating is usually later,
March to April, and closer to the time of egg laying (Fig. 41).
Drobysheva (1957) found that fully formed spermatophores are present
in male Thysanoessa inermis and T . raschii in the Barents Sea in
January and February but that mating does not take place until April
when the eggs are laid. Mating in Euphausia superba seems to take
place, like that of Meganyctiphanes norvegica, several weeks before the
eggs are laid (Bargmann, 1945). The data of Baker (1959) on the
breeding of Euphausia triacantha is not tabulated but from his description it seems that the males carry fully formed spermatophores for
some time before mating takes place and that a further period elapses
before the females lay their eggs. Although Nemoto (1957) presents
some data on the percentage of female Thysanoessa inermis, T . lolzgipes,
and T . spinifera that are fertilized during the summer months in the
North Pacific, he does not give any figures for the percentage of males
carrying spermatophores.
It can be concluded, however, from these descriptions that considerable variation between species, and probably within species in different
The spermatozoa do not appear to have any flagella.
THE BIOLOGY OF EUPHAUSIIDS
only the right side was developed and another one in which both sides
had produced spermatophores. I n E. krohnii, he finds that both the
left and right series of testicular vesicIes develop but that the right vas
deferens is very much reduced with hardly any lumen. The right
spermatophore sac is present but is also reduced and is only capable of
producing very small spermatophores which contain only a few spermatozoa. No comparable assymetry of the male copulatory organs was
present.
They are
spherical in shape, and in Meganyctiphanes norvegica have a diameter
of 9 p when they are released from the testicular vesicles but by the
time they reach the spermatophore sac their diameter has increased to
about 1411.. Most of them are still spherical but from here onwards
they are compressed into various shapes because they become packed
in the spermatophore which is being formed.
There is no detailed information on how the male uses the petasmae
to transfer spermatophores to the female. The shapes of the male
petasmae and female thelyca are peculiar to each species but how these
peculiarities function in the act of mating is unknown.
Mating of M . norvegica usually takes place in February in the Clyde
and nearly every female has spermatozoa present in the thelycum by
the end of February (Fig. 41) although the eggs are not usually laid
until the beginning of April. On the other hand, spermatophores are
formed by male Thysuno&sa raschii in the Clyde at the same time,
February, as by Meganyctiphanes norvegica but mating is usually later,
March to April, and closer to the time of egg laying (Fig. 41).
Drobysheva (1957) found that fully formed spermatophores are present
in male Thysanoessa inermis and T . raschii in the Barents Sea in
January and February but that mating does not take place until April
when the eggs are laid. Mating in Euphausia superba seems to take
place, like that of Meganyctiphanes norvegica, several weeks before the
eggs are laid (Bargmann, 1945). The data of Baker (1959) on the
breeding of Euphausia triacantha is not tabulated but from his description it seems that the males carry fully formed spermatophores for
some time before mating takes place and that a further period elapses
before the females lay their eggs. Although Nemoto (1957) presents
some data on the percentage of female Thysanoessa inermis, T . lolzgipes,
and T . spinifera that are fertilized during the summer months in the
North Pacific, he does not give any figures for the percentage of males
carrying spermatophores.
It can be concluded, however, from these descriptions that considerable variation between species, and probably within species in different
The spermatozoa do not appear to have any flagella.