104
THE BIOLOUY OF EUPHAUSIIDS
retaining their original structure, natatory. Anterior pairs of legs
and pleopoda successively developing.
5. Cyrtopia stage. Antennular flagella becoming elongate and
distinctly articulate. Antennae transformed, so as not to serve the
purpose of locomotion. Posterior legs and gills successively
appearing.
6. Post larval stage. All the legs developed. Telson assuming its
definite form and armature.
Stage 5, the cyrtopia, is not used now and the larvae which were
originally classed in this stage are included with the stage 4 larvae as
furciliae. The furciliae are the most interesting of all the larval stages
because easily noticeable variations in their development within and
between species are present. There are now available many descriptions
of these larvae belonging to many species but before examining these
later stages of development the eggs, spermatozoa, and embryos should
be considered first.
There are 85 species of euphausiids and of these 57 shed their eggs
freely into the sea. The remaining 28 species, comprising the genera
Nematobrachion, Nematoscelis, Nyctiphanes, Pseudeuphausia, Stylocheiron, and Tessarabrachion, protect the embryos until a nauplius
larva emerges. These eggs are attached to the posterior pairs of
thoracic legs.
The process of maturation of the ovaries is well known in Euphausia
superba, Meganyctiphanes norvegica, Thysanoessa inermis, and T . raschii
and follows the same general pattern in all these species (Mauchline,
1968). The ovary is very small at first and lies against the posterior
regions of the hepatopancreas beneath the pericardium and heart. The
volume of the ovary of Meganyctiphanes norvegica increases by five or
six times between November and January and the ovary consists of the
ovarian tissue itself and several thousand very small eggs, about
0-03 mm in diameter, which are being continuously released from the
germinal sites throughout this time. The germinal sites are located on
the ventral side of the developing ovary in all species investigatedStylocheiron spp. (Chun, 1896), Meganyctiphanes norvegica (Raab, 1915 ;
Mauchline, 1968) , Thysanoessa raschii (Mauchline, unpublished) , and
Euphausia superba (Bargmann, 1937). Raab (1915) describes the
arrangement of the eggs in the ovary of Meganyctiphanes norvegica in
great detail. The eggs, on release from the germinal sites, are found
all over the ventral area of the dorsal side of the ovary and extend into
the lateral or lobed regions, these lobes being follicles whose arrangement in groups gives the ovary its saddle shape (Fig. 37). The ovary
THE BIOLOUY OF EUPHAUSIIDS
retaining their original structure, natatory. Anterior pairs of legs
and pleopoda successively developing.
5. Cyrtopia stage. Antennular flagella becoming elongate and
distinctly articulate. Antennae transformed, so as not to serve the
purpose of locomotion. Posterior legs and gills successively
appearing.
6. Post larval stage. All the legs developed. Telson assuming its
definite form and armature.
Stage 5, the cyrtopia, is not used now and the larvae which were
originally classed in this stage are included with the stage 4 larvae as
furciliae. The furciliae are the most interesting of all the larval stages
because easily noticeable variations in their development within and
between species are present. There are now available many descriptions
of these larvae belonging to many species but before examining these
later stages of development the eggs, spermatozoa, and embryos should
be considered first.
There are 85 species of euphausiids and of these 57 shed their eggs
freely into the sea. The remaining 28 species, comprising the genera
Nematobrachion, Nematoscelis, Nyctiphanes, Pseudeuphausia, Stylocheiron, and Tessarabrachion, protect the embryos until a nauplius
larva emerges. These eggs are attached to the posterior pairs of
thoracic legs.
The process of maturation of the ovaries is well known in Euphausia
superba, Meganyctiphanes norvegica, Thysanoessa inermis, and T . raschii
and follows the same general pattern in all these species (Mauchline,
1968). The ovary is very small at first and lies against the posterior
regions of the hepatopancreas beneath the pericardium and heart. The
volume of the ovary of Meganyctiphanes norvegica increases by five or
six times between November and January and the ovary consists of the
ovarian tissue itself and several thousand very small eggs, about
0-03 mm in diameter, which are being continuously released from the
germinal sites throughout this time. The germinal sites are located on
the ventral side of the developing ovary in all species investigatedStylocheiron spp. (Chun, 1896), Meganyctiphanes norvegica (Raab, 1915 ;
Mauchline, 1968) , Thysanoessa raschii (Mauchline, unpublished) , and
Euphausia superba (Bargmann, 1937). Raab (1915) describes the
arrangement of the eggs in the ovary of Meganyctiphanes norvegica in
great detail. The eggs, on release from the germinal sites, are found
all over the ventral area of the dorsal side of the ovary and extend into
the lateral or lobed regions, these lobes being follicles whose arrangement in groups gives the ovary its saddle shape (Fig. 37). The ovary