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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which is obscured by the close opposition of its members; this apparently unpaired
muscle runs in the middle line obliquely from the ventral base of the caudal appendix,
over the receptaculum seminis, between the distal ends of the oviducts to the front
margin of the genital segment, where it is inserted at the posterior ends of the longitudinal
ventral muscles. Very feeble muscular strands, traversing the posterior part of the
genital segment, and inserted at the dorsal base of the appendix, seem to act
antagonistically to the great oblique muscle. On the ventral side of the genital
segment the fanshaped dilatator for the vulva, mentioned above, originates laterally in
the body-wall and is inserted in the thickened outer lip of the vaginal slit.
All the appendages are provided with intrinsic muscles; those of the antennæ
and thoracic limbs are feeble, those of the antennules stronger, and those of the
maxillæ very strong.
The whole muscular equipment apparently allows a certain amount of mobility
which hardly would be expected in an animal like this, confined inside a tightly
fitting capsule.
The adult male (Pl, I, Fig. 1, 4, 11, 12) is considerably smaller than the ripe
female, reaching at most a length of 2 mm. At first sight it seems very unlike the
female, slender, almost cylindrical, curved, and resembling an insect-maggot, but
closer inspection reveals fundamentally the same structure. The head takes up
between the third and fourth part of the total length; a carapace is distinctly marked
off, and trace of a rostrum may be seen between the antennules; the four thoracic
segments are very evident, the posterior one somewhat shorter than the three anterior;
taken together they make up the greater part, more than half the total length. The
body tapers evenly towards the abdomen. The latter is short, unsegmented (but also
here representing three segments, as shown by the larva). The part representing the
genital segment also in the male is by far the greatest and sends out on each side a
large outgrowth (1), conical, firmly chitinized and directed backwards, reaching (almost)
as far as the end of the tail; it corresponds to the clumsy lateral outgrowth in the ripe
females, and resembles — to a certain degree — that of the youngest unripe females,
as upon the whole the general likeness with the latter is more conspicuous. Ventrally
the genital segment carries genital openings (Fig. 11, go); they form large
crescent-shaped slits, arched over by the lateral opercular lips into which a special levator
muscle (Fig. 4 dil) is inserted. Towards the medial margin of the opercle short rows
of small hairs are found, at the posterior corner generally a larger spine or bristle
(largest in young individuals). The posterior end of the tail (ap), corresponding to
the “appendix” of the female, and representing two segments, forms a short narrow
part, terminating in two bifurcated claws; the outer one of each of these is generally
somewhat larger, the inner one provided ventrally with small hairs or bristles. In
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