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 the results 

 at which I had arrived during my studies of the s t r a c o d s' adaptation to a planktonic life. 

 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 s t r a c o d group to the theory put forward 

 b y R. WOLTERECK, 1913, of the function of the ,,sogen. Schwebe-Fort- 

 siitze pelagischer Cladocere n", as the results attained bv 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: 



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

 between littoral life and planktonic life. This transition can perhaps be best studied in the 

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

 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. „Chydorus sphaericus 

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

 mittels kraf tiger Ruderschliige durch das Wasser trJigt.'" 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 tlie 

 original one for the group 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 



[ntroductory 

 remarks. 



.4n account of 



H. Woltereck's i'ieu'. 



The original method 



of preven t ing s in king 



in the Cladocera. 



