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Bygning som hos de 2 foregaaende Slaegter; men (ie er forholdsvis mindre kraftigt udviklede,
og de til Svømmegrenen faestede Børster er ualmindelig korte, med (’dieringen grovere og
mindre taet. I Virkeligheden kan flisse Lemmer hos Hunnen kun uegentlig kaldes
Svømme-antenner, da tle ikke benyttes til Svømning, men kun som et Slags Arme .... ved Dyrets
langsomme krybende \ evaegelser paa Havbunden.“* The drawing with which G. 0. Sars
illustrâtes this description shows an antenna of about the same structure as the larval one.
i. e. with relatively short, unbroken bristles, well pointed distally, on the exopodite; curiouslv
enough in this drawing all the bristles of the exopodite have natatory hairs. From this
description and figure it seerned to me probable that the peculiarity of breaking-ofï the
natatory bristles would also be a characteristic of this species. In order to be absolutelv
certain on this point I wrote to Professors G. O. Sars and G. S. Brady asking for permission
to investigate their specimens. Both these investigators were kind enough to send me several
specimens. Among the specimens sent by Professor Sars there was only one (probably) mature
female; this specimen unfortunately, however, was represented only by two empty valves.
Among Professor Braüy’s specimens there was a complete female with verv large eggs in the
brood chamber. Contrary to G. 0. Sars’s statement this specimen had, on the exopodite of
the second antenna, like Ph. (Scleroconcha) Appellöfi, relatively short and quite bare bristles
on the second to the fourth joints; the bristles on the folio wing joints were long natatory
bristles of the same type as in the female of Pli. (Ph.) (jlobosa during its pelagian stage.
What is the connection between these facts and the view put forward bv G. \V. MOLLER,
1908, that the peculiarity of breaking ofï the natatory bristles in the genus Philomedes is not
a phenomenon of convergence, but that it is to be referred to a common inheritance?
It is obviously difficult to fit them in with this theory. Philomedes (Scleroconcha) Appellöfi
and Ph. (Ph.) rotunda represent two types rather strongly difïerentiatecl from Ph. (Ph.) globosa
and Ph. (Ph.) assimilis; the first-mentioned species especially differs comparatively greatlv
from the others. In ail these four forms the natatory bristles are broken ofï. In Ph. (Ph.)
Euqeniae, which is certainly very closely related to Ph. (Ph.) globosa and Ph. ( Ph.) assimilis.
and in Ph. (Sel.) Folini, which is very closely related to Ph.(ScL) Appellöfi the natatory bristles
remain nnbroken throughout the whole life.
Contrary to G. \Y. MULLER’s view, it seems to me necessary to assume that the peculiar
character of breaking off the natatory bristles of the exopodite of the second antenna in the
genus Philomedes is not the resuit of common inheritance but of convergence.
It is of course impossible at the present time to give any certain causes for this
phenomenon. The following facts are, however, striking:
1) All the species (five) of this genus from warm or temperate seas that were
in-vestigated with regard to this character proved to have long, unbroken natatory bristles
during the whole year.
* The second pair of antennae in the female certainly show, on the whole. the same structuro as in the two
preceding genera; but they are comparatively less powerfully developed, and the brist les that are attached lo the
natatory brandi are unusually short, with their hairs coarser and situated loss densely. As a matter of fai t these
limbs in the female cannot really be i alled swimming antennae, as they are not usod for swimming. but only as a sort
of arms .... in lhe animai s slow elawling movemonts al lhe bottom of the sea.
The breaking ojj oj
lhe natatory bristles
a phenomenon of
convergence?
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