Sliiilics on ninrinf Oslranids 25 



and e n d i t e s u r between these and t li e distal p a r t of t li e j) r o t o- 

 podite. These terms seem to be merely expressions for a classi- 

 fication of parts of the same organ which were originally 

 similar, a classification based on the relative position of the 

 parts to each other and to the organ, the limb considered as a 

 w h 1 e. The probability of this assumption ought to be obvious to anyone who has made 

 a thorough comparative morphological study of the post-oral limbs of the Phyllopods. 



The problem of the phylogeny of the Crustacean post-oral limbs must consequently 

 as yet be considered as being far from settled. Our knowledge of the types of limbs that 

 characterized the Protostraca, the hypothetical ancestral forms of the Crustacea, is still rather 

 uncertain. The homologization of the different parts of the limbs in different Crustacean 

 groups in many cases cannot be said to be proved. 



Is it possible to carry out a certain homologization of the 

 different parts of the multiform post-oral limbs of theOstra- 

 c o d s? In other words is it possible to carry out for this group as well the terminology 

 employed above? 



In discussing this very complicated problem we must, I think, pay special attention The principles used 

 to the fact that, as I have iust pointed out, there was presumably no essential and fundamental '/". '.*""'! '",/"""" 



. . ' logtzing the different 



difference originally between the different parts of the limbs, the epipodites, the exopodite, parts of tlie Umhs. 



the endopodite and the endites. The cause of their varied differentiation probably lies chiefly 



in their different positions. Thus the endites that were situated inside were destined to serve 



as organs for taking up food, the distally situated exo- and endopodites to develop into loco- 



motory organs, natatory, crawling or climbing organs, the lateral epipodial appendages were 



to become especially respiratory organs of one sort or other. 



Looking at it from this point of view, it can by no means be considered surprising or 

 improbable if it should turn out that the exopodite of one limb were differentiated to fulfil a 

 function which was connected with, let us say, the endopodite in the case of another limb of 

 the same species or of the same Umb in another group, or if the exopodite and the epipodial 

 appendage of different limbs of the same species were differentiated in corresponding ways 

 for the same function. As is shown by the following facts it may be considered quite certain 

 th.it instances of such conditions occur in the Ostracods: In Thaunrntocypris and Pobj- 

 oopw/ae both the exopodite and the endopodite of the second antenna are developed for a natatory 

 function; in the C y p r i d i n i d s and most of the H a 1 o c y p r i d s the exopodite alone 

 has taken over this function, the endopodite has been more or less reduced and adapted 

 to quite different functions; in tlie males, for instance, it is used as an organ for 

 seizing the females. In the C y p r i d s the endopodite of this antenna is adapted in 

 a number of forms both for crawling and for swimming- in other Cyprids, as well as in the 

 Ne side ids and Cy the rids, this branch is exclusively a crawHng organ; in these 

 three groups the exopodite is more or less completely reduced. In the Cytherellids 

 l)oth the exopodite and the endopodite are very powerfully developed and both of them are 

 crawling and digging organs. 



4 

 Zoolog. bldrag, Uppgaln 3uppl.-Bd. I. 



