Sluilics on iiiiiiiiir ()sli-;i(i)ils i'{ 



„Di<' Ausgangsform des Crustaceenbcincs, die jedonfalls auE eiii Aiuu'lidciiparapodiuiii zuriick- 

 t'uhrhar ist, diirfte die eines zweigliedrigen Blattes sein, dessen proxiniales Glied noch unvoll- 

 koinmen vom Korper getrennt ist iind seine Muskulatur aus diescm empfangt, wahrend das 

 distale Gliod noch ungegliedert ist und einen dorsalen blattformigpti Anhaiig triigt." (See fig. [.) 

 \\"it!i legard to the epipodial appendages this writer assumes, contrarv 

 to the iwo preceding writers but similarly to C. Claus, that they are 

 j.besondere Erwerbung der P h y 11 o p o d e n und L e p t o s t r a k eii "" 

 (p. 466): as an argument for this he adduces tlie relatively late appearance 

 of these organs during the ontogeny. 



With regard to the views of the three last-mentioned writers I wish 

 to quote a statement of W. T. Calman. This author writes, 1909 a, i). 9: "^ 



_ " 12 1 1 .1 j.-j^, J — Diagraiii of Uic 



,.it does not seem prohtable .... to attempt, as some have done, to („.igi„al type of the post - 

 compare the limbs of the Branchiopodu in detail with the Polvchaete oral Cnistaroan limbs, 

 parapodiiim". It is to be noted that in the Archiannelida, the Annelid '"'f"'''^'"^' '° ■• ^"\l''':' 

 group with the simplest structure, — whether this sim])licity is original j). '.f.7). 



or secondary seems to be uncertain as yet — there are no parapodia at 



all. E. KORSCHJSLT and K. Heider have not attempted to give any more detailed reasons for 

 their view — their statement is probably to be considered more us a whim than as a serious 

 hypothe.sis. 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 fact 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 lind^ has — according to the first mentioned opinion — dev(4oped from ffomologizatifm o, 

 the foliaceous limb. No agreement has. however, been yet reached as to whicli parts of the ''"^ '''Z/'"'"'"'" /""■'■'"j 



^ _ -^ '^ lliese types. 



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 played in this 

 development. As, early as 1881, in U.W Laxke.ster's essay on ,,Appendages and 

 nervous system of Afus cancriformis'\ this author put forward the assumption that of 

 the six endites that characterize ,.tlie 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. IT. This view has been accepted in many quarters. On the other hand \V. GlESBRECiri 

 assumes in his work of 1913 — following J. TllIELE — that the end part of the protopodite corre- 

 sponds to the endo[)odite; the exopodite, according to this author, corresponds to the distal exite. 



This uncertainty will be by no means surprising to those who have studied the mor- 

 phology of the foliaceous limbs of the P h v 1 1 o p o d s and have observed the great difficulty 

 that is attached to carrying out a certain homologization of tlie lobes and processes of the 

 different limbs in the different sub-groups of this group. See A. Behnixg. 1912. 



It is supposed that the third main type of post-oral limbs, the rod-shaped limb, has 

 arisen by the reduction and disappearance of one of the two branches of the biramous limb. 

 Whether, as is now generally assumed, (cf. W.GiESBRECHT, 1913, p. 32) it is always the exopodite 

 rliat disappeared, seems, according to what I believe I have observed, to be rather \mcertain. 



