Full resolution (JPEG) - On this page / på denna sida - I. Description of the developed (imaginal) stages of Chordeuma obesum n. g., n. sp.
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the matter by which the eggs after extrusion loosely cohere, and corresponding to
the substance secreted in other Copepoda by the same part of the oviduct and
generally forming the “ovisacs”.
The distal end of the oviduct suddenly narrows into a very small pore opening
in the short vagina (Fig. 8, vg); the latter has a chitinous lining continuous with the
outer genital slit. Like this the vagina in transverse section is crescent-shaped, the
lateral wall or outer lip being strongly thickened, completely filling out the concavity
of the half-moon (Fig. 10); a strong muscle, serving as dilatator (dil, Fig. 10), is inserted
in the outer, lip. Just at the same spot where the oviduct opens in the vagina,
debouches also a narrow and short duct from a large, unpaired receptaculum seminis
(Fig. 8, rs). The latter is rounded or pear-shaped, with one pole imbedded between
the distal ends of the oviducts, the other projecting backwards into the genital segment;
its front end and the distal ends of the oviducts are surrounded by a mass of large
unicellular glands. In females with eggs in the oviduct the receptacle and its ducts
always have been found filled with sperma; in young, unripe, females with empty
oviducts no sperma have been found, only a secretion, which seems not capable of
staining (produced by the unicellular glands ?).
Thus in the Parasitic Copepod before us the following features may be pointed
out as unusual: 1) an unpaired receptaculum seminis with paired outlets, one to
each opening of the oviduct in the vagina; 2) absence of separate copulatory pores.
Separate copulatory pores (or a single pore) are generally supposed to be typical
in Parasitic Copepoda, although their existence in many cases has not been proved
(Giesbrecht 10, p. 190—191 throws some doubt upon their occurrence in certain
Asterocheridae).
In Chordeuma the same slits, through which the eggs are laid, undoubtedly also
serve for copulation. I have examined the region in question very carefully, and
besides I have seen in some specimens spermatophores fastened into the genital (or
vaginal) slits (comp. Pl. I fig. 13 spf).
Alimentary canal. (Pl. I Fig. 8). Behind the rounded upper lip (ul) the
narrow mouth-opening leads into a short, slit-like pharynx, lined with a continuation
of the outer cuticle. Muscles pass obliquely behind the root of the upper lip and
are inserted into the roof of the pharynx; a little further back other muscles are
inserted in its floor, taking their origin laterally and from behind; both sets act as
dilatators, antagonistically counteracted by the elasticity of the chitinous lining of the
pharynx; thus a sucking process may be brought about. The pharynx is continued into
a short and slender, cylindrical oesophagus (oe), passing through the central nervous
system (nv) and opening in the ventral side of the stomach (in). The epithelial wall
of the oesophagus consists of comparatively high cells, arranged in a single layer round
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