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The post-oral limbs of t he 0 s t r a c o d s are, as has just been pointed out, exceedingly
inultiform ; the same limb often appears in such different types in the different groups that
a certain homologization of its different parts seems to be almost hopeless. As a matter
of faet the Ostracod group comprises such heterogeneous elements that one cannot expert
a priori to find any far-reaching morphological agreement between actually homologous organs.
Innervation, musculature, the number of joints, the bristle equipment, in other words the
anatomical characters that are concerned, often completely fail to give a certain due to the
homologization.
A 11 h o u g h facts obtained from comparative morphologv
and embryology have as far as possible been taken i n t o
considération in discussing these problems, the determining factor
h a s been, under these c i r c u m s t a n c e s, the position of the parts
dealt w i t h, t h e i r relative position t o e a c h other as well as t h e i r
position in relation t o the limb taken as a w h o 1 e. The results
o f homologizations c a r r i e d o u t on so s 1 i g h t a basis as the
positions m u s t, o f course, b e b o t h uncertain and u n s a t i s f a c t o r y
in m a n y cases*; this is still more so as the situation of the different parts of the limbs
is by no means constant.
G. W. MÜLLER, the only author who has discussed this problem in detail for the O s t r
a-c o d s, does not show quite clearly what principles he has followed in working it out. But
this writer seems, at least in some cases, ckiefly to hâve followed the last principle put forward
by me above, i. e. the positions of the different parts has been taken by this author too as
the determining factor. In other cases, on the contrary, other principles have been the dominant
ones for this writer. As a result of this he has in many cases, as is shown below, arrived at
results quite different from those put forward in this work.
Second antenna: — With regard to this limb I follow almost entirely the
terminologv found in G. W. MUller’s large treatise of 1894. According to this author this
antenna is a biramous limb, consisting of a protopodite, an exopodite and an endopodite; on the
other hand there are no epipodites and endites at ail. The protopodite is sometimes
single-jointed, sometimes two-jointed, sometimes it even has an indication of a third joint. The
exopodite and endopodite are developed very differentlv in different groups; sometimes both
these branches are well developed, as in Thaumatocypris, the Polycopids and the
Gy th erellids, sometimes the exopodite dominâtes decidedly over the endopodite, as, for
instance, in the Cypri d i n i d s and most of the H a 1 o c y p r i d s; sometimes the exopodite
is very much reduced, the endopodite on the other hand, very large and powerful, as in the
( y y> r i d s, D a r w i n u 1 i d s, N e s i d e i d s and C y t h e r i d s. i
Before G. W. MÜLLER it was assumed that the natatory brandi in the Cypridinids,
H a 1 o c y p rids and P o 1 y c o p i d s represented the endopodite, the other branch the
0 The difficulty or earrying out a terminology, based on a certain homologization, for the different parts of the
Ostrai’od limbs. corresponding lo that whieh has been accepted for other Crustacea may perhaps seem to justifv the use.
d Last for the present, of a quite neutral terminology for this group. The reason why this method has not been chosen
in th- present work is that because, in my opinion, it would only increase the confusion in these questions.
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