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of species belonging to this genus; cf. also G. W. MÜLLER, 1894. pl. 15, fig. 31. One of tliese
groups is situated antero-distally on the joint and comprises two claw-like bristles, the other is
situated postero-distally and consists of three bristles, one of which is a sensory bristle of about the
same type as the sensory bristle of the fourth joint in the genus Macrocypris and other C y p r i d s.
The two groups are separated from each other by a distinct swelling in the wall of the joint,
Can we, in the face of these facts, accept the homologization worked out by G. \V. MÜLLER
for these joints of these two families? I believe not. It seems far more probable — not
to say absolutely certain — that the joints in the family Nesideidae that are denoted by G. W.
MULLER as nos. 2 and 3 are homologous with the second joint in Macrocypris, the fourth joint
in the Nesideids corresponds to the third and fourth joints in Macrocypris. If we assume
this homologization we shall find the following points of agreeinent: The second joint is elongated;
it has on the posterior side proximally of the middle one or two bristles and on the anterior
edge somewhat proximally of the distal boundary two bristles situated close together. The
third joint is relatively short; it is moved by two muscles, a flexor and an extensor, both of
which have their proximal attachments proximally on the second joint; distally-anteriorly it
is armed with claw-like bristles. In Nesideidae, as in several C y p r i d s, the fourth joint is
completely reduced, but the bristles that belong to this joint can be distinguished from those
of the original third joint by means of a swelling in the wall of the joint; one of the bristles
of the fourth joint is a sensory bristle. In other words the agreement is complete. The lack
of resemblance if we accept G. W. MÜLLER’s homologization is as striking as the similarity if
we accept that worked out above. The same correction must also be made in G. \V. MüLLER’s
homologization of the endopodite of the second antenna in the C y t h e r i d s. This will
indicate the degree of certainty in the facts on which G. W. MÜLLER has based his
assiimp-tion with regard to the number of joints in the endopodite of the second antenna of the
Protostracods!
It is quite impossible at present to carry out a homologization between the joints of
the endopodite in all the groups of the Ostracods; we get no help at all from the characters
of bristles and muscles.
If, looking at these facts, we ask what is the number of joints that is to be taken
as the most primitive for the endopodite, whether this branch was originally characterized
by two, three, four or five joints, I think we shall be compelled to aeknowledge that this
is a question we cannot yet decide with any degree of certainty.
The exopodite of the second antenna of the Protostracods is supposed to
have been composed of a rather large number of joints, about the same as in the case of the
recent C y p r i d i n i d s, H a 1 o c y p r i d s and Polycopids. No proof of this is given by
G. W. MÜLLER. Among the recent Ostracods we apparently find nine joints constantly in all
representatives of the three above-mentioned groups; the Cytherellids have a powerful,
two-jointed exopodite; in all other Ostracods this branch has no joints and is more or
less completely reduced. Thus from comparative morphology we cannot — at least at present
produce any facts that indicate with any degree of certainty the number of joints that is to
be taken as the original one for this branch. Nor can any such facts be obtained from com-
Zoolog, bidrag, Uppsala. Suppl.-Bd. I. 11
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