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in the forms with two protopodite joints, is usually somewhat smaller than the part that
corresponds to the coxale and lias disto-anteriorly remains of endites, which are armed with a few bristles.
Apart from these this joint is quite without bristles. The epipodial plate is elliptically
oblong, situated vertically on the part of the protopodite that has been assumed above to be
homologous with the coxale, and is joined to this throughout its length; along the posterior
cdge it has a moderate number of marginal bristles, arranged in three groups which are in most
cases clearly distinct. These bristles are furnished along the greater part of their length with
moderately long, fine, sti fT hairs, placed close together and arranged in the form of a feat her.
The endopodite, which is moved by special muscles and projects rather far in between
the protopodite and the exopodite, is armed with a rather large number of bristles. The e x
o-p o d i t e is rather thick proximally and grows rather rapidly and uniformly thinner distally.
Its end joint, armed with three bristles, is always very small.
See p. 46 above for the difference between the ideas of previous writers as to the
morphologica! value of the various parts of this limb and the ideas about this problem that are
expressed in the description given above.
Sixth limb: — This limb, too, is subject only to rather slight variation within
this group. In the females it seems to serve chiefly as a climbing organ, in the males often
as an auxiliary organ in swimming, but in some cases, in the males of the genera Arckiconchoecia
and Halocypris, genera which show only rather slight or no dimorphism in this limb, it is, as
in the females, chiefly a climbing organ; on the other hand it never seems, either in males or
females, to be used in mastication or taking up food. It is situated on the side of the body,
just behind the fifth limb. It is always rather large and has well-developed musculature; it
is always stronger and larger in the male than in the female. It is constructed according to
the same type as the fifth limb, consisting of a voluminous, rather elongated, ventrally pointing
protopodite, which is sometimes more or less distinctly two-jointed, but in most cases unjointed,
and which is always somewhat shorter than the exopodite, a moderately large epipodial
append-age that is developed as a vibratory plate, a very short, unjointed endopodite (sometimes not
bounded ofî from the protopodite and then not possible to establish) and a four-jointed,
backward or backward-upward pointing exopodite, which is in most cases somewhat more
elongated in the males than in the females. Protopodite: This is of quite the same
type as the one on the fifth limb; like the latter, it is closely joined to the body
proximo-medially, but it is quite without any trace of endites. The epipodial appendage has
about the same size, type and position as this organ on the fifth limb; it differs from this chiefly
by the number of the bristles. The endopodite projects somewhat fart her in between
the protopodite and the exopodite tlian on the fifth limb; its muscles are very much reduced
or are even quite absent; it has only a very small number of bristles. As in the case of the
preced-ing limb the exopodite is rather thick proximally, and grows rather rapidly and
uni-formly thinner distally. Its end joint, armed with three bristles, is always small.
For the differences in the ideas about the different parts of this limb held by previous
writers and those put forward in the present work see p. 50 above, the chapter on the general
morphology of the limbs.
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