CHAPTER III. 



Contributions to our knowledge of the Ostracods' 

 adaptation to a planktonic life. 



It was at first my intention to put forward even in this part of my work all tlie results introductory 

 at which I had arrived during my studies of the Ostracods' adaptation to a planktonic life. remarks. 



But because of the great space demanded by the other chapters of this work and the difficulties 

 in printing that are now prevalent, it seemed to me best to postpone for the present the publi- 

 cation of a portion of these results. Here I shall only try to show briefly 

 the relation of the Ostracod group to the theory put forward 

 b y R. WOLTERECK, 1913, of the function of the „s o g e n. S c h w e b e - F o r t- 

 satze pelagischer Cladocere n", as the results attained by me with regard to 

 this question seem to be of such general interest that a rapid ^publication of them 

 seems desirable. 



First I shall give an account of R. Woltereck's view: -■'" aeco""' of 



A number of forms in the Cladocera are at present, as it were, at a transitional stage ' " '^'^^'^ * ""' ' 



1 1- 1 i-n T 1 1 • 1- ■ mi • • • The original method 



between littoral hie and planktonic lite. This transition can perhaps be best studied in the of presenting sinkin" 

 genus Chydorus, for instance in Ch. sphaericus. This species still lives to some extent the life '" '''<" Cladocera. 

 that is presumably the original one for the Cladocera, namely a crawling and jumping life at 

 the bottom or on the water vegetation in the littoral region. Sometimes, however, it swims, 

 and then it occasionally penetrates into the pelagian region of the lakes. „Chijdorus sphaericus 

 bewerkstelligt die Eroberung der pelagischen Region dadurch, dal3 er seinen schweren Korper 

 mittels krjiftiger Ruderschlage durch das W'asser tragt." This form is, however, not entirely 

 independent of the substratum even during its pelagian excursions; now and then it has to 

 rest on foreign floating objects, e. g., clusters of algae, etc. 



The method by which this form prevents itself from sinking down during its pelagian 

 excursions, i. e. self-motion, swimming, is, according to R. Woltereck, certainly the 

 original one for the groujj Cladocera. 



This method of preventing sinking represents, however, a serious consumption of energy. 

 — A closer study of the plankton world of our seas and lakes shows how the organisms 



