studies on mnriiio Osfrafods 65 



In answering this question it will be best first to try to show which characters in the 

 Ostracods are to be regarded as primitive. Or in other words what was tlie 

 organization of the original Ostracods, the- P r o t o s t r a c o d s? 

 On what lines has the development of the Ostracods proceeded? 



In investigating these problems we get no help at all from palaeontology. Represen- T^'x^ organization of 

 tatives both of G. \^'. Muller's group Podocopa and of Myodocopa are probably found even "'" ^'""''''■"""^'■ 

 in Lower Silurian. Almost always shells alone are known. 



It is very difficult to draw any conclusions as to the structure of the Protostra- 

 c o d s from the organization of other Crustacean groups, as our knowledge of the genetic posi- 

 tion of the Ostracods is anything but certain. I shall only give here as examples the 

 views of two of our foremost Crustacean investigators. * C. GROBBEN assumes, 1892, that the 

 Ostracods and the Cladocers have come from the same forms as the Conchostraca, 

 while C o p e p o d s, C i r r i p e d s and Branchiura are more closely related to Notostraca, 

 and Leptostraca and Malacostraca are joined to Anostraca. W. Giesbrecht assumes, on tlie 

 other hand, 1913, pp. 230 — 233, that Phyllopoda Anostraca, Notostraca and Conchostraca, Clado- 

 cera and Ostracoda form a special branch from Protostraca and that the Ostracods have 

 branched out from this ,,als dieser in der Richtung auf die Phyllopoden etwas iiber die 

 Abgangsstelle der Copepoden hinausgewachsen war". Thus, according to this writer, 

 Phyllopoda Anostraca, Notostraca and Conchostraca and Cladocera are comparatively closely 

 related to each other; on the other hand they are comparatively remote from the Ostracods 

 even though they are nearer to this group of animals than any other recent Crustacea. 

 According to W. GlESBRECHT it is difficult or even impossible at present to decide which of 

 the four groups just mentioned is most closely related to the Ostracods. 



The prevalent uncertainty in our knowledge of the organization of the Protostraca, the 

 hypothetical primitive forms of the Crustacea, ought also to be mentioned. I shall only 

 point out here the uncertainty with regard to the structure of the limbs of these forms. It 

 may be sufficient in this connection to refer to what is written on this problem on pp. 22 — 24 

 above. The main object of this somewhat detailed exposition is to give the reader an idea of 

 the great uncertainty with regard to this important problem. 



In dealing with the problem of the organization of the P r o t o s t r a c o d s we 

 are thus entirely or at any rate almost entirely confined to a comparison of the morphology 

 and embryology of the recent Ostracod groups. 



It ought perhaps to be pointed out at the very outset that the result of this 

 investigation is bound to be rather uncertain, both on account of the 

 great difficulties of the problem and the uncertainty and incompleteness of our knowledge 

 with regard to much that concerns the organization and embryology of these groups of animals. 



The only author who has closely studied the problem of the organization and development 

 of the P r o t o s t r a c o d s is G. W. MCller. In his large monograph of 1894, pp. 191—199. 

 this writer has given a very detailed account of the results he obtained during these investi- 

 gations. Other authors touch on this question more cursorily; I need only mention here, among 



* Cf. also C. Claus's view. 187fi. p. 91 ami W. Giesbreciit's remark on Ibis. 1893. p. 88, reinark. 



q 



Zoolog. bidrag, tJppsBla. SiippI -Bd I. 



