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the stems of the members of the same pair are connected by a transverse crest,
projecting from the ventral side of the segment in question. The rami are flat, oblong,
each made up of one segment; the outer ramus (y) is considerably larger than the
inner (i) and on the distal part of its inner arched margin beset with four long and
stiff bristles (in a single case I found five on the third pair): at the end of the straight
or feebly concave outer margin a fifth short bristle is present. The short and narrow
inner ramus (i) is terminally provided with three bristles, of which two belong to the
inner, one to the outer margin. The bristles have no plumules, while plumules are
present on the two pairs of furcal setæ, of which the inner ones are the longest.
There are no furcal appendages, the setæ originating directly from the posterior
margin of the telson.
As the tissues of these larvæ were rather badly preserved, I have not been able
to make out inner structural details of any amount, in spite of my transverse and
longitudinal sections being quite successful. Distinctly discernible are: the narrow
oesophagus leading into the wide intestine (mid-gut), closed behind in the thorax, about
at the level of the third pair of swimming feet; and the central nervous system,
consisting of the large brain and the ventral ganglionic mass, narrowing towards the
first pair of thoracic feet; further back I have not been able to trace it. The presence
of antennal or shell-glands as well as of rudiments of genital organs I cannot state
with certainty.
The Cyclops-larva moults and changes into the seventh stage, the parasitic form
described sub I. This is sufficiently proved in the case of the male by the fact,
already stated, that quite a number of extremely small males — like that represented
Pl. II, Fig. 26 — have been found together with the ruptured cuticle of the
Cyclops-larva, in some cases with the tail still lodged inside the latter; and in a single case
a very small female was found near an empty larval cuticle. In all cases observed
the formation of a gall was indicated as a condensing of the connective tissue
surrounding the young parasite and the cast larval cuticle. After the moulting through
which the parasite form ensues, no further moultings take place, but the Copepod
and its gall continue for a while to grow considerably; during the growth the parasite
undergoes some slighter modifications in shape of body and appendages, as shown
above sub I, and develops its inner structures; finally it attains full size and sexual
maturity.
| Concluding remarks. |
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