406 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Rotifera. 



Rotifera and Gastrotricha of Germany.* — Part 14, recently issued, 

 of Brauer's Collectors' Guides to the Fresh-water Fauna of Germany, 

 contains an account and short diagnosis of Rotifera and Gastrotricha 

 so far found in Germany. With 265 pages of text and 507 figures, it 

 forms a very useful and most complete guide! for the ready identifica- 

 tion of the majority of species. 



Biolog-y of Pond Rotifers,! — As the resuit of two years of con- 

 tinuous study of the life-history and behaviour of Rotifera, their food, 

 variations, vertical and horizontal distributions in ponds and small 

 bodies of water, as contrasted with larger lakes, H. DiefFenbach and 

 and R. Sachse have reached the following important conclusions : — 



1 . The increase or decrease of the zooplankton in ponds is directly 

 controlled by the abundance or scarcity of centrifuge plankton, which 

 forms the main food of the majority of Rotifers. 



2. Nutrition has a great influence on the normal size of Rotifers ; 

 with sufficient food material in the shape of centrifuge plankton, no 

 reduction, or a very slight one only, takes place from generation to 

 generation in the usual size of Rotifera. When food material is very 

 plentiful the body, lorica and appendages may experience an increase 

 in length ; when food material is deficient, a reduction in size follows 

 rapidly. The influence attributed in this connexion to changes of tem- 

 perature is non-existent. 



3. The distribution of pelagic Rotifera is entirely dependent upon 

 that of centrifuge plankton. During the day the vertical distribution of 

 both the pelagic Rotifera and centrifuge plankton is unequal. The 

 greatest abundance of plankton life is found in a zone which lies about 

 half a metre below the surface of the water. During the night the 

 vertical distribution becomes uniform throughout the water — that is, the 

 centrifuge plankton diffuses through all layers and the Rotifera follow 

 their food. Horizontally, the distribution is uniform during day and 

 night for pelagic Rotifera. 



4. The influence of nutrition also shows itself in the cyclical varia- 

 tion of various species in which variations from the normal form coincide 

 with variations in the abundance of food material. 



5. In the family of the Brachionidai, consisting of pelagic {Brachi- 

 onus angularis), semi-pelagic {B. pala) and littoral forms B. bakeri and 

 B. urceolaris), the distribution is unequal, depending on the distribution 

 of food material suitable for the respective species. The region of the 

 centrifuge plankton is the region of the pelagic species, which feed on 

 these organisms exclusively ; the region of centrifuge plankton and 

 detritus is that of the semi-pelagic species, and the detritus region is 

 that of the littoral forms. 



6. Seasonal variations and the appearance of appendages in succes- 

 sive generations (such as those of B. pala-amphiceros) occur at times of 



* Die Susswasserfauna Deutschlands. Heft 14, Rotatoria und Gastrotricha 

 (Jena, 1912) 265 pp. (507 figs, in text). 



t Intern. Rev. Ges. Hydrobiol. u. Hydrog. Biol., Supp. 3 (1911, published 1912) 

 pp. 1-93 (6 pis.). 



