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that which characterizes the recent Cypridinids; there are both anatomical and
mechani-cal reasons against this. This method of swimming seems to présupposé the dominance of the
exopodite. This circumstance seems also to have been noticed by G. W. MÜLLER; this author
writes, 1894, p. 193, as follows:* „Daß bei einer fast ausschließlichen Verwerthung der 2. Antenne
als Schwimmfuß der Innenast schwindet, scheint verständlich, denn er verdankt seine Erhaltung
als kleiner Rest nur der Function als Greiforgan beim und dürfte diese bereits bei der
gemeinsamen Stammform der Myodocopa besessen haben.“ It will probably be sufficient to point
out in this connection that all the forms that swim in this way (all the Cypridinids,
all the genera of Halocyprids except Thaumatocypris) have the endopodite reduced;
this branch does not help as a natatory organ. On the other hånd, in Thaumatocypris and the
P o 1 y c o p i d s, which are, as we know characterized by another method of swimming, both
the exopodite and the endopodite are always well developed.
It seems to me most probable that the rostral incisur swimming is a later acquisition.
It even seems not impossible that this method of swimming has arisen and been developed
independently in the two groups, Cypridinids and Halocyprids. This idea seems
to be decidedly supported by the faet that Thaumatocypris, the genus that is in many respects
the most primitive of all the Halocyprids, does not have this method of swimming, but
swims in quite a different way. It must, of course, be considered as very improbable — not
to say entirely impossible — that the Cypridinids diverged from the Halocyprids
a f t e r Thaumatocypris.
Can we assume that any other of the three methods of swimming described above as
occurring in the recent Ostracods is primitive in this group?
It seems to be impossible to assume that the method of swimming that characterizes
the genus Thaumatocypris is original; as far as I can see this method needs long processes on
the shell (cf. below, the chapter on adaptation to a planktonic life) and such processes could
scarcely have characterized the shells of the Protostracods.
There remains consequently only the method of swimming that we fourni as characteristic
of the Polycopids and a number of the C y p r i d s. But it does not seem possible to
consider this either as primitive in the Ostracods, as both the position of the P o 1
y-c o p i d s and the C y p r i d s in the Ostraeod system and the details in the development of
this mode of swimming seem to support very decidedly the idea that this mode of swimming
has arisen and been developed independently in these two groups.
Is it not really at least equally probable that the ancestors of the Ostracods were
not freely swimming but crawling forms — although their powers of crawling were not quite so well
developed as in a number of recent forms, e. g. N e s i d e i d s and C y t herids? By this
i do not, of course, mean to state decidedly that they had a crawling life and that they lacked
all power of swimming, but I only wisli to point out that this possibility does not seem to me
exeluded. Before we have succeeded in showing quite definitely that this possibility is out of
the question it does not seem right to put forward an assumption that the opposite state of
affaire is the correct one — at least the matter should not be put in such as definite way as
" I leiivc* a l loge ther out of consideratiori Un* illogieal déduction in this statement.
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