studies on marine Ostracods 49 



reproduced here, of the sixth limb in the same group. From this comparison it will be seen 

 that, in spite of profound difEerences, 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, lamellifonn process; in the 

 next larval stage ifis two-lobed distally, with 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. MOller, 1894, pi. 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 imsettled. 



In dealing with the morphology of this limb, just as in the case of the others, the prece- Historical. 



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 him- 

 self 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 either.* 

 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. 

 MaxiUarfuB von Cypris, sowie an das diesem gleichwerthige vordere Beinpaar von Halocypris, 

 ohne jedoch morphologisch diesem (5.) Gliedmafienpaar zu entsprechen." The small collection 



* It is true that G. O. Saks 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-ni paris 

 prodeuntes, . . . posteriores apici appendicum penultimi paris affixao, iiiferne vergenles, triangulares, verlicales, juxta- 

 positae." But it is quite clear, however, from his statements on pp. 41 and 42 in the same work that this is not the 

 case. He shows here that the part of the fifth limb which has been explained by me above, according to the so- 

 called first method of explanation, as the third and fourth exopodite joints — it is described by G. O. SAE8 as a 

 ,,tyndt og gjennemsigtigt membrai;0st W'dhang" (a thin, transparent, membranous appendage) — is most probably 

 homologous to „den saakaldte Vifteplade (lamina vibratoria) paa det felgende 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 \. M. Xorma.n'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 penultimate 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 arc 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 wTilers have not even attempted to 

 form any opinion at all of the Iiomology of these organs, 



Zoolog. bidrag, Uppsala. Suppl.-Bd. I. ' 



