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G. W. MÜLLER ,seems to have suspected the weakness of this assumption himself, as he writes
„vermuthlich“ before it. In dealing with this problem the following facts ought to be noted:
There are only two groups among the recent Ostracods, namely the Cypridinids
and the H a 1 o c y p r i d s, which are characterized by having a rostral incisur. The
Cyprids, Darwinulids, Nesideids, Cytheri ds, Cytherellids and
Polycopids of which the latter group is considered. presumably correctly, to be rather
primitive in many respects, and Thaumatocypris, presumably the most primitive genus among
the Halocyprids, have not this peculiarity in their organization. The rostral incisur
in the C y p r i d i n i d s is presumably not homologous with that of the Halocyprids.
In the Halocyprids the rostral incisur has been partly formed by the outer lamella of
the shell having been bulged out like a finger of a glove into a sort of rostrum near the dorsal
boundary of the anterior margin of the shell; the margin of the shell continues, as G. W. MULLER
himself pointed out in his monograph of 1894, p. 101, in the form of an s-shaped bent line
„Buchtlinie“ (C. CLAUS), situated basally on the inside of the rostrum. In the Cypridinids,
on the other hand, the incisur is formed simply by a concavity of the anterior margin of the
shell. In the face of these facts and as there seem to be no reasons to support G. IV. MüLLER’s
assumption, it does not seem too bold to draw the conclusion that the rostral incisur
is not a character which belonged to the Protostracods.*
Whe thus see the failure of the strongest — and as far as I can see the only — argument
in favour of assuming that the Protostracods had a method of swimming of the
same type as that of the recent Cypridinid s. There is, in addition, at least one more
reason that seems to contradict this assumption. G. W. MÜLLER assumed that the second
antenna of the Protostracods had both the exopodite and the endopodite well
developed and thatboth these branches were used in swimming (cf. G. W. MÜLLER, 1894, p. 199);
this antenna seems to resemble most closely the recent Polycopids. The assumption that
the second antenna originally had both the exopodite and the endopodite well developed seems
to me justified; there are several arguments in favour of this. First, the exopodite dominâtes
in a number of forms (Cypridinids and most of the Halocyprids), while the
endopodite dominâtes in others (Cyprids, Darwinulids, Nesideids and C y t
heri d s), secondly, a number of forms, Thaumatocypris, Polycopids and C y there
1-1 i d s, have a second antenna with both the exopodite and the endopodite well developed.
On the other hand it seems to be very unlikely that the two branches took part in swimming,
at least if we assume the same method of swimming for the Protostracods as
* In this connection I ought perhaps to mention the statement put forward by C. Clals. 1876, p. *j, to the
effect that the deep concavities found behind the „ear-shaped lobes“ anteriorly on the shells of larvae of the Dichelopod
genus Euphausia are récurrences of the rosirai incisurs in C y p r i d i n i d s and II a 1 o c y p rids and are of great
value phylogenetically. This author writes as follows on this point: „Von Interesse scheint mir das Vorhandensein zweier
ohrförmiger Lappen an dem als Kragen bezeichneten Abschnitt der Panzerduplicatur. Eine tiefe Einbuchtung,
hinter jedem der beiden Seitenlappen ist eine Wiederholung des Ausschnittes an der Schale der Cypridinen und
Halocypriden, und weist mit vielem anderen darauf hin, daß wir den Malacostrakenpanzer und die
Schalenbildungen der Eutomostraken von gleichem Ausgangspunkt abzuleiten haben.“ 1 give this statement for what
it is worth. I ought perhaps to mention, however, the great variation shown in the shape of the Shells of larvae belonging
to Malacosiraca. Wh y should just the peculiar type of shell in this genus be of great phylogeneli« value?
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