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.
In answering this question it will be best first to try to show which characters in the
Ostracods are to be regarded as primitive. Or in other words what was the
organization of the original Ostracods, the - Protostracods?
On what lines has the development of the Ostracods proceeded?
In investigating these problems we get no help at all from palaeontology. Represen- The
tatives both of G. W. MÜLLER’s group Podocopa and of Myodocopa are probably found even
in Lower Silurian. Almost always shells alone are known.
It is very difficult to draw any conclusions as to the structure of the
Protostracods from the organization of other Crustacean groups, as our knowledge of the genetic
position of the Ostracods is anything but certain. I shall only give here as examples the
views of two of our foremost Crustacean investigators. * C. GROSSEN assumes, 1892, that the
Ostracods and the Cladocers have come from the same forms as the Conchostraca,
while Copepods, Cirripeds and Branchiura are more closely related to Notostraca,
and Leptostraca and Malacostraca are joined to Anostraca. W. Giesbrecht assumes, on the
other hånd, 1913, pp. 230—233, that Pliyllopnda Anostraca, Notostraca and Conchostraca, C
lado-cera and Ostracoda form a special branch from Protostraca and that the Ostracods have
branehed out from this ,,als dieser in der Richtung auf die P h y 11 o p o d e n etwas über die
Abgangsstelle der Copepoden hinausgewachsen war“. Thus, according to this writer,
Phyllopoda Anostraca, Notostraca and Conchostraca and Cladocera are comparatively closely
related to each other; on the other hand they are comparatively remote from the Ostracods
even though they are nearer to this group of animais than any other recent Crustacé a.
According to W. GIESBRECHT it is difficult or even impossible at present to decide which of
the four groups just mentioned is most closely related to the Ostracods.
The prévalent uncertainty in our knowledge of the organization of the Protostraca, the
hypothetical primitive fonns of the Crustacé a, ought also to be mentioned. 1 shall only
point out here the uncertainty with regard to the structure of the limbs of these forms. It
may be sufficient in this connection to refer to what is written on this problem on pp. 22—24
above. The main object of this somewhat detailed exposition is to give the reader an idea of
the great uncertainty with regard to this important problem.
In dealing with the problem of the organization of the Protostracods we
are thus entirely or at any rate almost entirely confined to a comparison of the morphologv
and embryology of the recent Ostracod groups.
It ought perhaps to be pointed out at the very outset that the result o f this
investigation is bound to be rat her uncertain, both on account of the
great difficultés of the problem and the uncertainty and incompleteness of our knowledge
with regard to much that concerns the organization and embryology of these groups of animais.
The only author who has closely studied the problem of the organization and development
of the Protostracods is G. W. MÜLLER. In his large monograph of 1S94. pp. 191—199.
this writer has given a very detailed account of the results he obtained during these
investigations. Other au thors touch on this question more cursorily; I need only mention here, among
* GL also C. Clads’s view, 1876. p. 91 and W. GiEsnnF.ciiT’s remark on this. 1893. p. 88. remark.
Zoolog. bidrag, TTppaala Suppt -IM I.
organization of
Protostracods.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
