MICROSCOPIC AQUATIC ORGANISMS. 365 



observations of the ordinary kind required on large numbers 

 of species of all classes, but entirely new methods of investigation 

 will have to be devised, and very considerable improvements 

 of old methods, such as instantaneous photography, etc., carried 

 out, before we can hope to solve the many interesting problems 

 presented to us in connection with the movements of living 

 organisms in water. In fact, there is work here for many 

 scientific labourers, professional and amateur alike, whether 

 having command of the highest powers of the microscope or 

 limited to the lowest, whether mainly interested in experimental 

 investigations or content to take Nature's gratuitous statements 

 without further questioning. 



The following list of literature, although very imperfect, will 

 probably be found helpful by those who may wish to go into this 

 subject more deeply than it has been possible to do in the present 

 paper. 



Bethe, A. " U eber die Erhaltung des Gleichgewichts," Biologisclies 

 Centralblatt, Bd. 14, 1894, pp. 95-114, and 563-82. 



(Gives results of many experiments as to specific gravity of 

 aquatic animals, their means of orientation, maintenance of 

 equilibrium, etc.) 

 Butschli, O. " Protozoa " in Bronn's Klassen und Ordnungen 

 des Thier-Reichs, 1880-9. 



Abt. I. Sarkodina and Sporozoa, pp. 114 et seq., 284, 



442 (amoeboid motion). 

 Abt. II. Mastigophora, pp. 846 et seq., 956, 1085, 



(flagellate motion). 

 Abt. III. Infusoria, pp. 1788 et seq. (ciliate motion). 

 Butschli, O. Untersuchungen uber mikroskopische Schdume und 

 das Protoplasma, 1892. English translation, Investigations 

 on Microscopic Foams and on Protoplasm, 1894. (Records 

 the results of experiments with "artificial Amoebae.") 

 Calkins, G. N. The Protozoa, 1901. (Contains remarks on the 

 structure and action of pseudopodia, pp. 79-86 ; flagella, 

 pp. 119-23 ; and cilia, p. 181.) 

 Jennings, H. S. " Asymmetry in Certain Lower Organisms and 

 its Biological Significance," Mark Anniversary Volume, 1903, 

 Art. xvi. pp. 315-37. (An interesting paper dealing with 

 spiral structure and spiral locomotion.) 



