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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an extremely narrow space. The stomach (in) is a capacious, pear-shaped sac, tapering
backward and ending blindly in the last thoracic segment; it has a single layer
of rather flat epithelial cells. It always contains an ovoid body, concentrically
composed of layers, probably indigestible matters deposited as a kind of “stone”, as
there is no practicable way to get rid of any faeces. In some cases this “stone” may
be large enough to be seen with the naked eye.
Nervous System. (Fig. 8). The brain (cb) is situated dorsally to the antennæ,
close in front of the oesophagus; it is rounded and provided with a coating of ganglionic
cells; a short, rather broad commissure on each side of the oesophagus connects
with the ventral nerve-mass (nv.); the structure of the latter is the same as that of
the brain; it lies dorsally to the maxillæ and tapers into a thread coated with
nerve-cells and reaching at least through the first and second thoracic segments. From
each side of the brain a long nerve is seen going to the antennules; from the broad
anterior part of the ventral mass other nerves are going to the maxillæ, but the
greater part of the peripheral nerves I have not been able to make out.
Muscles. (Fig. 8). The muscles of the body form quite narrow ribbons, isolated
from each other by considerable interspaces. The longitudinal muscles are made up of
four dorsal and two ventral ribbons. The former — one pair of dorsal (md), and
one of latero-dorsal (mdl) muscles — take their origin from the inner concave surface
of the head in the region of the ovary and stop at the last thoracic segment, being
divided for each segment by an insertion in its front margin. The latero-dorsal
pair are a little stronger than the dorsal. The ventral pair (mv) take their origin
inside the head near the middle of the base of the maxillae; from here they diverge
feebly in the head and first thoracic segment, are almost parallel in the second and
converge evenly through the third and fourth, almost meeting at the same point of
insertion in the front margin of the genital segment. Thus the abdomen has no
longitudinal muscles of its own but is acted upon by means of those of the trunk,
the flexors acting directly, the extensors indirectly.
There are several pairs of transverse and oblique muscles originating dorsally or
dorso-laterally in the head and thorax and inserted at the base of the appendages;
some of them seem to be fastened rather to the body-wall near the limbs than
directly into the latter, and it is not quite clear to me, how they may act on the
appendages. Most of these muscles belong to the head and first thoracic segment,
and here they run obliquely in different directions (cf. Fig. 8), some of them more
superficially than others and therefore more easily seen. In each of the three last
thoracic segments only one pair of strictly transverse muscles is found, running
deeply on each side, between the stomach and the oviduct.
In the abdomen a set of deep strong muscles is observed, the paired nature of
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