Sliiilios on inaiini^ Osliiiroils -•! 



,,Dio Aus<!;angsf()nii dps frustacocnbcines, die jedenfalls auf ein Annelidcnparapodiuiii ziuiick- 

 fiihrbar ist, dihfte die eincs zweiglicdrigen Blattes sein, dessen proximales Glied ncjch unvoll- 

 kommen vom Korper gptrennt ist mid seine ^Tuskulatur aiis diesem empfangt. wahrend das 

 distale Glied iioch ungegliedert ist iind eiiien dorsalen blattformigen Anhang triigt." (See fig. I.) 

 With regard to the epipodial appendages this writer assumes, contrary 

 to the two preceding writers but similai'lv to C. Claus, that they are 

 j.bcsondere Erwerbung der P li y 1 1 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 relatively late appearance 

 oi: 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. Cat.man. This author writes, 1909 a. p. 9: ,r' , , . , ,, 



^ .1 I'lg. I. — Diagram of llv 



,.It does not seem profitable .... to attempt, as some have done, to original type of the posi- 

 compare the limbs of the Branchiopoda in detail with the Polychaete "''^' Crusiarean limbs. 



,.,.-. , , , • 1 < 7 ■ 7-7 11 1-1 aicording to .1. Tiiif.i.k. 



parapodmm . It is to be noted that in the Archunmeiida, tite Annelid (|.-,.„„, j T,i,Kr.F. \wr>. 

 group with the simplest structure, — whether this simplicity is original \>. 'ifi:). 



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



all. P>. KORSCHELT and K. Heii'ICH 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. Thielk has tried to produce arguments for his opinion, but 

 his demonstration is anything but convineins. .\s 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 limb has — according to the first mentioned opinion — developed from Homologization nj 

 the foliaceous limb. No agreement has, however, been vet 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 played in this 

 development. As early as 1881, in Rav LaxkESTER's essay on ..Appendages and 

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

 the six endites that characterize ..the second thoracic foot'" of this species no. 5. counting proxirao- 

 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. CtIESBRECH'i 

 ass\imes in his work of 1913 — following J. TlIIELK — that the end part of the protopodite corre- 

 sponds to the endopodite; 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 the lobes and processes of tht- 

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



It is supposed that the third main type of po.st-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. Giesrrecht, 1913, p. 32) it is always the exopodite 

 that disappeared, seems, according to what I believe 1 have observed, to be rather uncertain. 



