Full resolution (JPEG) - On this page / på denna sida - II. The development
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hosts are provided with an enormous number of this parasite, and why these are to
be found of very different age and size. In the latter case the larvæ might most
easily make their way out through the bursal slits, and in spite of their lack of eyes
they may find without great difficulty new Asteronyx, as these animals cling to the
often densely congregated sea-pens. The way leading to the interior of the new hosts,
I think again would be the bursal slits. In both cases the larva is supposed to attach
itself by means of its hooked maxillæ, either among the genital sacs of the host, or
on that face of its intestinal wall, which looks towards the bursal pouch, or on the
inner dorsal body-wall, and the stimulation due to this fixation may cause the tissues
to produce a gall. Quite exceptionally the larva may fix itself on the outer surface
of an Asteronyx; this is shown by the few cases of external galls mentioned before.
That the larvæ should be able to make their way to the interior of the host by
active working through its body wall (f. ex. through the dorsal wall, the inside of
which is often studded with parasites), seems to me most improbable. How far the
course of things here set forth will prove to be the right one, I hope will be tested
some day by others, who may have the luck of investigating the living animals
in their mutual relations.
The Cyclops-larva (Fig. 22—23) has a length of 0,304—0,320 mm from the front
to the end of the telson (of this the tail takes up only ca. 0,072 mm; the furcal setæ
have about the length of the tail). The general shape is that of a Cyclops; the trunk
is ovoid, somewhat compressed laterally; the short and slender abdomen is often
directed obliquely upwards. The head has a carapace distinctly marked off, with a
short, rounded rostrum, curved down between the antennules; the thoracic segments,
especially the three last ones, are sharply defined; the belly is arched; hence the body,
seen in profile, is rather high. The antennules are strong and — as far as I have
made out — composed of seven joints, the outermost one long and transversely cut
at the end; each joint is provided on its front side with a seta, some of the basal
joints with two setæ; the terminal joints have besides setæ on their back; the
ultimate, penultimate and the fourth (from the tip) carry each a large “aesthetasc” (ae)[1].
The antennæ (a2) are short, slender, three-jointed (the outer branch of course is
absent); the last joint with two terminal setæ. Mandibles, maxillulæ and eyes are
absent. The maxillæ (mx) are very strong, composed of three segments, the terminal
a hooked claw. Each of the four thoracic swimming feet (Fig. 24) has a well
developed basal stem (b) and two rami (y and i) of unequal length; as usual in Copepoda
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