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„Die Ausgangsfonn des Crustaceenbeines, die jedenfalls auf ein Annelidonparapodiuni
zuriiok-tührbar ist, dürfte die eines zweigliedrigen Blattes sein, dessen proximales Glied noch
unvollkommen vom Körper getrennt ist und seine Muskulatur aus diesem empfängt, während das
distale Glied noch ungegliedert ist und einen dorsalen blattförmigen Anhang trägt.“ (See fig. I.)
With regard to the epipodial appendages this writer assumes, contrarv
to the two preceding writers but similarlv to C. CLAUS, that they are
,.besondere Erwerbung der P h y 11 o p o d e n und L e p t o s t r a k e n“
(p. 466); as an argument for this he adduces the relativelv late appearance
of these organs during the ontogenv.
With regard to the views of the three last-mentioned writers I wish
to quote a statement of W. T. Calmax. This author writes, 1909 a, p. 9:
,.It does not seem profitable .... to attempt, as some have done, to
compare the limbs of the Branchiopoda in detail with the Polychaete
parapodium“. It is to be noted that in the Ardiiannelida, the Annelid
group with the simplest structure, — whether this simplicité is original
or secondary seems to be uncertain as yet — there are no parapodia at
all. E. KORSCHELT and K. HER »KR have not attempted to give any more detailed reasons for
their view — their statement is probablv to be considered more as a whim than as a serious
hypothesis. On the other hand J. THIELE has tried to produce arguments for his opinion, but
his demonstration is anything but convincing. As a matter of faet one cannot, when studying
his exposition, help reflecting that it would not be very difficult, using his method of proof and
other facts, to ,,prove“ other views of this question.
The biramous limb has — according to the first mentioned opinion — developed from
the foliaceous limb. No agreement has. however. been yet reached as to which parts of the
latter are to be considered as homologous with the exopodite and endopodite of the former
nor in general as to the part that the different parts of the foliaceous limb have plaved in this
development. As early as 1881, in Rv’i LaxKESTER’s essay on „Appendages and
nervons system o f Apus cancriformis“, this author put forward the assumption that of
the six endites that characterize ..the second thoracic foot“ of this species no. 5, counting
proximo-distally, is homologous with the endopodite and no. 6 with the exopodite; cf. the accompanying
fig. 11. This view has been accepted in many quarters. On the other hand W. GiESBRECin
assumes in his work of 19] 3 — following J. THIELE — that the end part of the protopodite
corresponds to the endopodite; the exopodite, according to this author, corresponds to the distal exite.
This uncertaintv will be bv no means surprising to those who have srudied the
mor-phology of the foliaceous limbs of the Phyllopods and have observed the great difficult y
that is attached to carrying out a certain homologization of the lobes and processes of the
different limbs in the different sub-groups of this group. See A. Behxixk. 1912.
It is supposed that the third main type of post-oral limbs, the rod-shaped limb, has
arisen by the réduction and disappearance of one of the two branches of the biramous limb.
Whether, as is now generallv assumed, (cf. W. Giesbrecht, 1913. p. 32) it is alwavs the exopodite
that disappeared, seems. according to what I believe I have observed, to be rather uncertain.
Kig. I. — Diagram of the
original type of the
postoral Crustacean limbs.
according to .1. Thiele.
(From .1. Thiele. 1905,
p.
H ontologi zat ion oj
Ihe dijferenl paris of
iltese types.
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