studios on mariiio Ostracods 57 



sclu'int bfiachtenswerth fiir die morphologische Deutung der (JliedmaaBen der Ostracoden. 

 Freilich fiir entscheidend fiir die Auffassung gerade des fraglichen Beinpaares halte ich ihn nicht. 

 Es sind da zahlreiche Moglichkeiten zu beriicksichtigen: so kann die GliedmaaBe in den Dienst 

 der Nahrungsaufnahme getreten sein, bevor die Schale den heutigen Umfang erreicht hatte, 

 oder es kann der eine Ast sich an der Nahrungsaufnahme betheiligt haben, bevor der andere als 

 Klammer- oder Schreitorgan Verwerthung fand, was durch die geringe GroBe des nach hinten 

 gerichteten Astes bei den H a 1 o c y p r i d e n vmd C y p r i d e n eine gewisse Wahrschein- 

 lichkeit gewinnt. Die Zahl der in Betracht kommenden Moglichkeiten liefie sich leicht vermehren; 

 aber bei der Unmoglichkeit, sich fiir die eine oder andere zu entscheiden, wird man am besten 

 than, ahnliche Gesichtspunkte bei derFrage nach der Deutung der Aeste aus dem Spiel zu lasscn. 

 Die Aehnlichkeit der Aeste verschiedener GliedmaaBen liefert immerhin noch den sichersten Anhalt. " 



With regard to this statement of G. W. MtlLLER's we may first point out the justice 

 of his objection to a quite uncritical application to the limbs of the Ostracod group of the rule 

 observed by W. GlESBRECHT for the anterior limbs in the Copepods. The conditions in 

 these two groups are certainly so different that what is a rule in one may very well be an ex- 

 ception in the other. On the contrary, every special case must be tested by itself as thoroughly 

 as possible. The necessity of this is probably best illustrated by the second antennae of the 

 Ostracods. 



On the other hand there is, as far as I can see, no evidence at aU for G. W. MOller's 

 statement that the development of the epimeres on the posterior cephalomeres into a shell 

 enclosing the whole body favours the development of the inner branch into a locomotory organ. 

 It can scarcely be thought that the shell was any absolute obstacle to an increase in the length 

 of an exopodite that was pointing obliquely backwards and outwards. At most, as is pointed 

 out above, this branch was forced by the shell to turn slightly backwards. The ,, evidence" in 

 favour of this statement of his obtained by the author from the exopodite of the second antenna 

 in Cypridinids, Halocyprids and P o 1 y c o p i d s is, of course, almost too 

 weak and transparent to need further discussion. To judge from the reservation he added, 

 G. W. MiJLLER himself realized this weakness. It will probably be sufficient to point out that 

 the exopodite of this antenna is used as a locomotory (natatory) organ, even in such forms 

 as have no rostral incisur, e. g. in Polycopidae and Thaumatocypris. The rostral incisur is not 

 to be considered as a structure that makes it possible for the exopodite on this antenna to 

 be used as a locomotory and natatory organ, but as a structure by means of which the second 

 antenna alone, without the help of the first antenna, may be able to fulfil the function of a loco- 

 .motory (natatory) organ; for tliis it is necessary that this limb shall be moved, not in the 

 sagittal plane, but straight outwards from front to back. This has already been pointed out 

 by G. O. Sars, 1865, p. 6 (cf. chapter III of this work), ^^'ith regard to the useless nature 

 of the rest of the above statement I am quite in agreement with its author. 



I can thus merely keep to my view as accepted above with regard to the explanation 77«- first method ■■/ 



„ , , . ^ , , .-11 /- 1 i ii 1 i- -i- explanation is ado [i- 



of these branches. In arnvmg at this I have been practically confined to the relative positions ^^^ .^ ^^^^ ^^^^^ 

 of the parts. In these cases other characters have ahnost entirely failed. Thus in the 

 present work the method of e x ]i 1 a n n t i o n accepted for the fifth, 



Zoolop. bidrap, tJppsala. Supp].-Bd. I. 



