SI\idii'S on iiiKrino Oslracfids 81 



of species belonging to this genus; cf. also G. W. MtlLLER, 1894, pi. 15, fig. 31. One of these 

 groups is situated antero-distally on the joint and comprises two claw-like bristles, the other is 

 situated postero-distally and consists of three bristles, one of which is a sensory bristle of about the 

 same type as the sensory bristle of the fourth joint in the genus Macrocypris and other C y p r i d s. 

 The two groups are separated from each other by a distinct swelling in the wall of the joint. 

 Can we, in the face of these facts, accept the homologization worked out by G. W. MUller 

 for these joints of these two families? I believe not. It seems far more probable — not 

 to say absolutely certain — that the joints in the family Nesideidae that are denoted by G. W. 

 MOLLER as nos. 2 and 3 are homologous with the second joint in Macrocypris, the fourth joint 

 in the N e s i d e i d s corresponds to the third and fourth joints in Macrocypris. If we assume 

 this homologization we shall find the following points of agreement: The second joint is elongated; 

 it has on the posterior side proximally of the middle one or two bristles and on the anterior 

 edge somewhat proximally of the distal boundary two bristles situated close together. The 

 third joint is relatively short; it is moved by two muscles, a flexor and an extensor, both of 

 which have their proximal attachments proximally on the second joint; distally-anteriorly it 

 is armed with claw-like bristles. In Nesideidae, as in several C y p r i d s, the fourth joint is 

 completely reduced, but the bristles that belong to this joint can be distinguished from those 

 of the original third joint by means of a swelling in the wall of the joint; one of the bristles 

 of the fourth joint is a sensory bristle. In other words the agreement is complete. The lack 

 of resemblance if we accept G. W. Muller's homologization is as striking as the similarity if 

 we accept that worked out above. The same correction must also be made in G. W. MlIller's 

 homologization of the endopodite of the second antenna in the C y t h e r i d s. This will 

 indicate the degree of certainty in the facts on which G. W. MCller has based his assump- 

 tion with regard to the number of joints in the endopodite of the second antenna of the 

 Protostracods! 



It is quite impossible at present to carry out a homologization between the joints of 

 the endopodite in all the groups of the Ostracods; we get no help at all from the characters 

 of bristles and muscles. 



If, looking at these facts, we ask what is the number of joints that is to be taken 

 as the most primitive for the endopodite, whether this branch was originally characterized 

 by two, three, four or five joints, I think we shall be compelled to acknowledge that this 

 is a question we cannot yet decide with any degree of certainty. 



The exopodite of the second antenna of the Protostracods is supposed to 

 have been composed of a rather large number of joints, about the same as in the case of the 

 recent C y p r i d i n i d s, H a 1 o c y p r i d s and P o 1 y c o p i d s. No proof of this is given by 

 G. W. MCller. Among the recent Ostracods we apparently find nine joints constantly in all 

 representatives of the three above-mentioned groups; the Cytherellids have a powerful, 

 two-jointed exopodite; in all other Ostracods this branch has no joints and is more or 

 less completely reduced. Thus from comparative morphology we cannot — at least at present — 

 produce any facts that indicate with any degree of certainty the number of joints that is to 

 be taken as the original one for this brancli. Nor can any such facts be obtained from com- 



Zoolog. bidrag, Uppsala. Suppl.-Bd. I. *^ 



