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see above, that the Protos t r a co ds had a fifth limb of about the same type as that
of the recent genus Macrocypris, but with a well-developed vibratory plate on the protopodite.
It seems to me very difficult to decide with certainty which of these views is correct. On
the one hand I consider it by no means impossible that the foliaceous type in the Cypridinids
may be original; this assumption agréés, of course, with the hypothesis that is almost
universally adopted nowadays, namely that the foliaceous type is the original one for this limb in
the Crustacea and that the rod-shaped limb is a secondary type developed from the foliaceous
one — in most cases via the biramous stage. On the other hand I think it far from
impossible that Gr. W. MÜLLER is nearest to the truth and that the foliaceous type is of a
secondary nature in the Cypridinids, that in this group this limb was shortened in
connection with its development as the most important or at any rate one of the most important
masticatory organs. It is obvious that G. W. MÜLLER based his assumption on the agreement
found between the fifth limb in the Halocyprids on the one hånd and this appendage in
C y p r i d s, Darwinulids, N e s i d e i d s and Cytherids on the other. This agreement is
certainly striking, but this is such a relatively simple organ that I can by no means consider it quite
impossible that the resemblance is due to convergence. See also below, the sixth and the
seventh limbs.
It is possible, however, that the foliaceous type is the original one and that the
rod-shaped type was developed from it, without it being necessary to assume that the
resemblance between the fifth limb in the Halocyprids and the C y p r i d s, etc. is
necessarily the result of convergence. This présupposés, however, that the ancestors of the
C y p r i d s, Darwinulids, Nesideids and Cytherids branched off from the
ancestors of the Halocyprids after the latter had been differentiated from the ancestors
of the Cypridinids.
With regard to G. W. MÜLLER’s assumption that the original number of joints on
the exopodite* of this limb was four I only wish to point out that this is partly based on
presumably incorrect homologizations. This writer states that the Cypridinids have four
joints on this branch; in doing so he counted the basale of the protopodite as the first
endo-podite joint, the first and second joints of the exopodite as joint no. 2; on the other hånd this
writer has not paid attention to the faet that there is sometimes an additional joint distally
of joint no. 4, sensu G. W. Müller I. According to this author the Halocyprids also
have four joints on this branch; he arrived at this number by counting the endopodite as the
first exopodite joint; ci. G. W. MÜLLER, 1894, p. 60. It is, however, to be noted that in one
genus of this group, which was not known to this writer when he put forward the assumption
discussed here, namely the genus Thaumatocypris, the exopodite has four joints; cf. G. W.
MÜLLER, 1906 a, pl. A I, fig. 3. This is noteworthy, as this genus is in many respects to be
consid-ered as the most primitive among the H a 1 o c y p r i d s. With regard to the uncertainty
of the homologization of this limb compare p. 54 above.
G. W. MÜLLER’s assumption that this limb was developed as a seizing organ in the
males of the ancestors of the forms which he groups together under the naine of Podocopa
* Explained by G. W. Müller as an endopodite.
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