Sliulies on aiariin' Oslracuds (W 



(!ra(lually, liowever, there came a natural reaction against tl\is mania for speculation. 

 During the last few decades the interest of biok)gists has been concentrated more and more on 

 more exact methods of investigation, especially experimental investigation. With the watch- 

 word ,,More facts, less theory" scientists have attacked, with brilliant results, such problems 

 as the conception of species, variability, heredity, the factors that produce species, etc. Beneath 

 the pressure of the multitude of facts discovered by scientists during this period a great 

 deal of the bold speculative fabric of the preceding jjeriod has collapsed piece by piece; manv 

 ,, pedigrees" and hypothetical original forms have been proved to be untenable. 



As a result of this reverse theoretical classification has been neglected, perhaps even 

 more than it deserved. A number of investigators have even expressed a wish that classification 

 should quite get rid of the theory of evolution and that it should only have as its aim a good 

 characterization and a lucid arrangement of the organic world; in other words they desire a 

 return to the tasks that the classifier formerly looked upon as his. 



It is certain that this is going too far. Only after the introduction of the principle of 

 evolution into classification can the latter be said to have been raised to the level of a science. 

 To separate these two things would certainly be a retrogressive step. I should like to quote 

 in this connection a statement of L. PLATE, 1914, p. 109: ,,Von jeder groBeren syste- 

 matischen Abhandlung sollte man erwarten, daJ3 sie mit phyletischen Betrachtungen ab- 

 schlieBt und aUe zurzeit vorliegenden Beobachtungen aus dem eigenen Untersuchungsgebiet 

 und aus verwandten Disziplinen (Anatomie. Embrvologie) zusammcntragt und nach dicsor 

 Richtung hin priift". 



In dealing with the theoretical problems connected with evolution it seems to be most 

 convenient to retain the method of working out hypothetical original forms — a crystaUizatif)ii 

 of the qualities that are assumed to be original — and ,, pedigrees" — graphical presentations 

 of the hypothetical genetic position of the different systematic units. The argument may gain 

 considerably in clearness by the use of this method. But a far deeper criticism must be made 

 than was formerly the case; the hypotheses must be founded on a very broad basis of facts; 

 it is best to stop when the facts cease to furnish distinct evidence. 



I shall attempt below to give an exposition of the natural system and the history of 

 the evolution of the Ostracods according to the results given by previous writers and 

 by my own studies of this group of animals. 



In all the works published before 1850 the s t r a cods were divided directly into History oj ihc i-,i- 



T , . 1 I iiT T^ , • , 1 XT ^ 1 IT • i '"■"' xyxtem fij ihn 



genera. In this year there appeared \\ . Baihd s important work „N a t u r a 1 History o.s(rn«rf.v. 



of the British Entomostrac a", in which this group of animals was divided into 

 three families: 



Familv I. Cypridae with the genera Cypris and Candona 

 „ II. Cytheridae ,, „ „ Cy there ,, CytJiereis 



III. Cypridinadae „ ,, genus Cypridina. 

 In J. D. Dana's large work on the Crustacea collected by the „U n i t e d States 

 Exploring Expedition" another important advance is to be noted, as the Ostra- 

 cods are here divided into two families, both of which are again divided into two sub-families: 



