72 TAOK SKOdSHKRO 



that wliich characterizes the recent C y p r i d i ii i d s; there are both anatomical and mechani- 

 cal reasons against this. This method of swimming seems to presuppose the dominance of the 

 exopodite. This circumstance seems also to have been noticed by G. W. MtlLLER; this author 

 writes, 1894, p. 193, as follows:* ,,DaB bei einer fast ausschlieBlichen Verwerthung der 2. Antenne 

 als 8chwimmfuB der Innenast schwindet, scheint verstandlich, denn er verdankt seine Erhaltung 

 als kleiner Rest nur der Function als Greiforgan beim ^ und diirfte diese bereits bei der gemein- 

 samen Stammform der Myodocopa besessen haben." It wiU probably be sufficient to point 

 out in tliis connection that all tlie forms that swim in this way (all the C y p r i d i n i d s, 

 all the genera of H a 1 o c y j) r i d s except Thaumatocypris) have the endopodite reduced; 

 this branch does not help as a natatory organ. On the other hand, in Thaumatocypris and the 

 Polycopids, which are, as we know characterized by another method of swimming, both 

 the exopodite and the endopodite are always well developed. 



It seems to me most probable that the rostral incisur swimming is a later ao(|uisition. 

 It even seems not impossible that this method of swimming has arisen and been developed 

 independently in the two groups, C y p r i d i n i d s and Halocyprids. This idea seems 

 to be decidedly supported by the fact that Thmmiatocypris, the genus that is in many respects 

 the most jjrimitive of all the Halocyprids, does not have this method of swimming, but 

 swims in quite a different way. It must, of course, be considered as very improbable — not 

 to say entirely impossible — that the C y p r i d i n i d s diverged from the Halocyprids 

 a f t e r Thauvnttocypris. 



Can we assume that any other of the three methods of swimming described above as 

 occurring in the recent Ostracods is primitive in this group? 



It seems to be impossible to assume that the method of swimming that characterizes 

 the genus Thaumatocypris is original; as far as I can see this method needs long processes on 

 the shell (cf. below, the chapter on adaptation to a planktonic life) and such processes could 

 scarcely have characterized the shells of the Protostracods. 



There remains consequently only the method of swimming that we found as characteristic 

 of the Polycopids and a number of the C y p r i d s. But it does not seeni possible to 

 consider this either as primitive in the Ostracods, as both the position of the Pol y- 

 c o p i d s and the C y p r i d s in the Ostracod system and the details in the development of 

 this mode of swimming seem to support very decidedly the idea that this mode of swimming 

 has arisen and been developed independently in these two groups. 



Is it not really at least equally probable that the ancestors of the Ostracods were 

 not freely swimming but crawling forms — although their powers of crawling were not quite so well 

 d(!veloped as in a number of recent forms, e. g. N e s i d e i d s and C y t h e r i d s? By this 

 I do not, of course, mean to state decidedly that they had a crawling life and that they lacked 

 all |)ower of swimming, but I only wish to point diit that this possibility does not seem to me 

 ex(;lude(l. Px'fore we have succeeded in showing quite definitely that this possibility is out of 

 the question it does not seem right to put forward an assumption that the opposite state of 

 affaii's is the correct one — at least the n\atter should not be put in such as definite way as 



~ I li.ivr all(ii;fUlM' iiiil or ciiiisidclMlidn lln- illiiyii.il ili'.liirl icii in lliis sl.i Iciilciil . 



