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reproduced here, of the sixth limb in the same group. From this comparison it will be seen
tkat, in spite of profound differences, these two limbs have the same fundamental plan; it
seems to me that the homologization of the different parts of one limb stands or falls according
to the homologization of those of the other. The great resemblance that exists between the
fifth and sixth limbs in the families Halocypridae, Cypridae, Darwinulidae, Nesideidae and
Cytheridae seems to justify us in drawing conclusions in the family Cypridinidae as well from a
comparison between these two limbs.
This limb begins embryologically as a simple, unjointed, lamelliform process; in the
next larval stage it is two-lobed distally, witli one rather large outer lobe, the end joint of the
complete limb and a smaller inner lobe, explained according to the interpretations given above
as the first joint of the exopodite (or the endopodite respectively). It is only later that the
proximal joints with their endites appear. Cf. G. W. MÜLLER, 1894, pl. 34, figs. 21, 22 and
24. Whether these embryological facts justify us in drawing any final conclusions in the
questions dealt with above I must leave unsettled.
In dealing with the morphology of this limb, just as in the case of the others, the
prece-ding writers have been rather superficial: most of them do not seem even to have tried to form
any idea as to the morphological value of the different parts of this appendage. We find
the following views in the previous literature: C. CLAUS, 1865, p. 151, seems to have had a
vague idea that the part of this limb in Cypridinidae that has been explained by me above
as the end joint corresponds to the vibratory plate on the preceding limb; he expresses
kimself so cautiously, however, that one cannot be quite certain about this — ,,welcher seiner Lage
nach an die schwingende Platte des vorhergehenden Kiefers erinnert“. C. CLAUS himself,
however, took up a definite position against this assumption as early as in his work of 1873
and this idea does not seem to have been seriously adopted by any of the other writers eitker.*
In the work just mentioned C. CLAUS writes as follows of this joint (p. 218): „In der
That erinnert die Stellung und Form dieser mehr oder minder dreieckigen Platte an den sog.
Maxillarfuß von Cypris, sowie an das diesem gleichwerthige vordere Beinpaar von Halocypris,
ohne jedoch morphologisch diesem (5.) Gliedmaßenpaar zu entsprechen.“ The small collection
* It is true that G. O. Sars in his work of 1887, p. 9 seems to adopt this explanation, as he writes as follows:
„Laminarum vibratoriarum 2 paria adsunt valde dissimilia, anteriores de basi appendicum antepenulti i i paris
prodeuntes, . . . posteriores apici appendicum penultimi paris affixae, inferne vergentes, triangulares, verticales,
juxta-positae.“ But it is quite ciear, however, from his statements on pp. 41 and 42 in Ihe same work that Uns is not the
case. He shows here that the part of the fifth limb which has been explained bv me above, according to the
so-called first method of explanation, as the third and fourth exopodite joints — it is described by G. O. Saks as a
„tyndt og gjennemsigtigt membraiøst Vedhang“ (a thin, transparent, membranous appendage) — is most proba bly
homologous to „den saakaldte Vifteplade (lamina vibratoria) paa det følgende Par Lemmer“ (the so-called vibratory
plate on the following pair of limbs). It is impossible to decide with certainty what is G. S. Brady and A. M. N’orman’s
view about this part of the sixth limb in their work of 1896. They have not made any distinct statement as to the
homo-logy of this organ — just as in the case of most of the other organs. In their description of Cypridina ( Vargula) norvegica
W. Baird we read on p. 648 with regard to this limb: „The penultiniale limbs or third maxillae end in three setiferous
lobes, the outer side of the limb carries a sub-triangular vibratory lamina, margined at first with nine plumose setae,
beyond which the margin is simply finely ciliated, while near the further angle are three more plumose setae.“ The
vibratory plate on the fifth limb is termed by these writers „vibratory plate“. The similar terms perhaps indicate that
these organs are considered to be homologous. It is possible, however, that these writers have not even attempted to
form any opinion at all of the homology of these organs,
Zoolog, bidrag, Uppsala. Suppl.-Bd. X.
Historical.
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