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apparent.
In the latter case, the 3 chief divisions, cephalon, mesosome and meta-
some, may, us a rule, be tolerably well distinguished, though not very sharply
defined from each other. Of appendages, the cephalon carries generally in
front two pairs of rudimentary antennae, and is produced below to a conical pro-
are much
minence exhibiting on the tip the oral aperture. The oral parts
reduced, only the mandibles and maxillipeds being distinctly developed,
the for-
mer being styliform and converging to the oral orifice, the latter lamelliform.
The legs, when present, are all alike, prehensile, terminating in a minute hand.
The pleopoda are in some instances rather large, and all of them branchial in
character, whereas in the larvae these organs are natatory. The uropoda, when
present, are always very small and simple, and do not in any
with the last segment
a caudal fan.
instance form
As to the systematical relation of this tribe to other Isopodous tribes,
Dr. H. J. Hansen has suggested, that it is closely related to the Cymothoidce and
cannot therefore be set apart from the tribe FlabeUifera. In this opinion I am,
however, by no means prepared to agree with the distinguished
Danish author.
The apparent resemblance to the CymotlioidoR is only due to the parasitic habits
of both ; but in the more essential points of organisation, as also in their develop-
ment, both these groups are in reality widely different, and no transition
forms between them are as yet known.
Of recent authors, who have made this tribe their special study, may
in the first place be named the two distinguished French naturalists M.M.
Giard and Bonnier, who have published several admirable treatises on these
interesting Isopoda, accompanied by
excellent illustrations. It is however to be
regretted, that these authors have introduced considerable confusion as to the
definition of species and genera, owing to an assumption, according to which
it is postulated, that one and the same species of parasite cannot be found
on different species of Crustacea, and that, as a rule, parasites infesting
different genera af Crustacea must also be generically different. This assump-
tion is most certainly unmaintainable, and a great number of species, and -
per-
haps also genera founded only upon this principle, must of course be cancelled.
The grouping of the several genera, into families has also to a great measure
been made according to a similar principle. No less than 7 families have thus
been established by the above-named authors, viz.
1. Microniscidos parasitic on Copepoda.
2. Cyproniscidce Ostracoda.
3. DajidcB Schizopoda.
4.
Cabiropsidce Isopoda and Amphipoda,