290
THE BIOLOGY O F EUPHAUSIIDS
measurements of Thysanogssa inermis, T . raschii, T . longicaudata,
Meganyctiphanes norvegica (Bogorov, 1939) ; twenty-nine measurements
of M . norvegica (Mauchline, 1967a) ; fifty measurements of Thysanoiksa
inermis, T . longipes, and Euphausia pacifica (Ponomareva, 1963) ;
fifteen measurements of Nyctiphanes couchii, Stylocheiron longicorne,
and Nematoscelis megalops (Shmeleva, 1965). The slope of the
regression line for weightllength is not great enough to fit the data
from the largest individuals. This change in slope is probably caused
by the presence of mature gonads, causing these animals to be relatively
heavier per unit body length than smaller animals. A similar change of
slope in the data on the volume/body length relationship is not evident.
The volume to body length relationship in fifty specimens of each sex
of Meganyctiphanes norvegica was examined and no sexual differences
in the relationship found (Mauchline, 1967a). Measurements of the
body volumes and lengths of specimens belonging to fifty species
representing nine of the eleven genera are presented (Mauchline, 1967a)
as follows : eight species of Thysanopoda, twenty species of Euphausia,
Pseudeuphausia latifrons, Meganyctiphanes norvegica, Nyctiphanes
couchii, Nematobrachion JEexipes, seven species of Thysanoessa, five
species of Nematoscelis, and six species of Xtylocheiron. I n all, 103
estimations were made and the data are presented in Fig. 110 as a
regression analyses for the Euphausiacea. If the regression line for
weight to body length is compared to this one then it can be seen that
they cross each other because their slopes are slightly different, but
because of the scatter in the results the difference is not significant.
The density of Meganyctiphanes norvegica is about 1.035 (Mauchline,
1967a) but this requires confirmation.
The growth rates of internal organs of the body relative to the body
as a whole have not been examined in euphausiids except in the case of
the ovary of Meganyctiphanes norvegica. The volume of the ovary
relative to the total body volume of the animal was measured in samples
of females over a period of several months and the mean percentage of
the body volume represented by the ovary in each month plotted
(Fig. 111). This, then, is the growth curve for the ovary. A further
analysis was made to discover the rates of growth of the eggs within
the ovary (Fig. 111). The growth rate of the eggs of Euphausia superba
in the Antarctic appears to be slower than those of the other species,
all from the northern hemisphere. This may be a fault in the data used
to compute the growth rate because Bargmann obtained the mean egg
size in E. superba at any one time by measuring a sample of the smallest
and a sample of the largest eggs in the ovary. Consequently, ripe eggs
of about 0.6 mm diameter are probably developed within the ovaries
THE BIOLOGY O F EUPHAUSIIDS
measurements of Thysanogssa inermis, T . raschii, T . longicaudata,
Meganyctiphanes norvegica (Bogorov, 1939) ; twenty-nine measurements
of M . norvegica (Mauchline, 1967a) ; fifty measurements of Thysanoiksa
inermis, T . longipes, and Euphausia pacifica (Ponomareva, 1963) ;
fifteen measurements of Nyctiphanes couchii, Stylocheiron longicorne,
and Nematoscelis megalops (Shmeleva, 1965). The slope of the
regression line for weightllength is not great enough to fit the data
from the largest individuals. This change in slope is probably caused
by the presence of mature gonads, causing these animals to be relatively
heavier per unit body length than smaller animals. A similar change of
slope in the data on the volume/body length relationship is not evident.
The volume to body length relationship in fifty specimens of each sex
of Meganyctiphanes norvegica was examined and no sexual differences
in the relationship found (Mauchline, 1967a). Measurements of the
body volumes and lengths of specimens belonging to fifty species
representing nine of the eleven genera are presented (Mauchline, 1967a)
as follows : eight species of Thysanopoda, twenty species of Euphausia,
Pseudeuphausia latifrons, Meganyctiphanes norvegica, Nyctiphanes
couchii, Nematobrachion JEexipes, seven species of Thysanoessa, five
species of Nematoscelis, and six species of Xtylocheiron. I n all, 103
estimations were made and the data are presented in Fig. 110 as a
regression analyses for the Euphausiacea. If the regression line for
weight to body length is compared to this one then it can be seen that
they cross each other because their slopes are slightly different, but
because of the scatter in the results the difference is not significant.
The density of Meganyctiphanes norvegica is about 1.035 (Mauchline,
1967a) but this requires confirmation.
The growth rates of internal organs of the body relative to the body
as a whole have not been examined in euphausiids except in the case of
the ovary of Meganyctiphanes norvegica. The volume of the ovary
relative to the total body volume of the animal was measured in samples
of females over a period of several months and the mean percentage of
the body volume represented by the ovary in each month plotted
(Fig. 111). This, then, is the growth curve for the ovary. A further
analysis was made to discover the rates of growth of the eggs within
the ovary (Fig. 111). The growth rate of the eggs of Euphausia superba
in the Antarctic appears to be slower than those of the other species,
all from the northern hemisphere. This may be a fault in the data used
to compute the growth rate because Bargmann obtained the mean egg
size in E. superba at any one time by measuring a sample of the smallest
and a sample of the largest eggs in the ovary. Consequently, ripe eggs
of about 0.6 mm diameter are probably developed within the ovaries