Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
It may, however, be pointed out here in passing that G. W. MULLER has assumed that
the brush-shaped organ might possibly be found in the males of the Cypridinids; he
writes as follows about this: „Man muß an die Möglichkeit denken, daß der Penis der
Cypri-d i n i d en daraus hervorgegangen ist, oder daß es in den Penis aufgegangen ist und einen Theil
desselben bildet. An dem Penis verschiedener Cypridiniden, nicht aller, läßt sich eine
borstentragende Platte nachweisen, welche bei Cylindroleberis“ (= Asterope) „entschieden an das
bürstenförmige Organ erinnert, dem sie auch in ihrer Lage im Wesentlichen entspricht.“
Without entering in any detail into this difficult problem I will only point out that these
assump-tions are to be considered as, to say the least, very uncertain — a faet that has, of course, been
admitted by G. W. Müller himself. If we regard the penis in the Cypridinids as
horno-logous to the brush-shaped organ, we pre-suppose, of course, that the former organ is not
horno-logous with the penis in the Cyprids, Nesideids, Cytherids and Cythere
1-1 i d s. It is true that some investigatore have denied the homology of these organs — because
the penis in the Cypridinids does not include the vas deferens — but this view seems
to be untenable for several reasons. It also seems to be very improbable that the bristle-bearing
plate on, for instance, the penis of Asterope is homologous to the brush-shaped organ. It seems
more probable that it represents one of the two branches of the biramous limb from which the
penis probably has developed; cf., for instance, G. W. Müller, 1894, pi. 5, fig. 41.
We thus find that the brush-shaped organ is situated in a number of forms close to the
fifth limb, in others close to or behind the seventh limb. Are these homologous organs?
G. W. Müller is of the opinion that they are because of the similarity in shape of the organs in
all the groups and also because in almost all the groups in which it has been observed, C y p r i d s,
Nesideids, Cytherids and Cytherellids, it is confined to the same sex. I
have nothing to add to this. At any rate the possibility is not exeluded. The position behind
the seven th limb is taken by G. W. MÜLLER to be the original one; the brush-shaped organ
would represent the eightli limb. With regard to the cause of the hypothetica! displacement
this author writes as follows, p. 76: „Die Bedingungen, welche das Organ zwischen die anderen
Beinpaare drängt, sind wohl in der Verkürzung des gesammten Körpers zu suchen. Nachdem
es einmal zwischen die Beinpaare gerathen war, wurde es bei den Formen, welche seitlich stark
comprimirt sind (z. B. Paradoxostoma) bei denen kein Platz mehr zwischen den der Mittellinie
sehr genäherten Beinen blieb, bis vor das vorderste Beinpaar gedrängt.“ In support of the
assumption that the position behind the seventh limb is the original one it may be pointed out
that the forms in which this position has been observed are considered to be more or less
primitive in several respects. It is perhaps also supported by the late appearance of this organ during
ontogeny; it appears only „wenn alleGliedmaaßen annähernd ihre definitive Form besitzen“; with
regard to the last argument it may, however, be pointed out that reduced organs often appear
com-paratively late, as, for instance, the reduced second maxilla in the Cladocera. Other authors assume
that the position in front of the fifth limb is original; according to these authors the brush-shaped
organ would represent the second maxilla of other Crustacea. No reasons of any importance have
been put forward in support of this view; on the other hand we must say, I think, that this
possibility must be regarded as being present. This problem thus seems so far to be unsolved.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
