400 S. J. HOLMES 



Von Prowazek's book ^' contains a valuable general account 

 of the physiology of the Protozoa, including their reactions 

 to various kinds of stimuli 



Experiments were made by Rose*" upon the various tropisms 

 of Daphnia longispina. The ordinar}^ positive reaction of this 

 species to light of moderate intensity can be made more vigorous 

 by the addition of small amounts of various acids and urea. 

 The Daphnias remain positive in NaOH and CaCb, but the 

 reaction is enfeebled in KCl. The author also studied the 

 influence of age, light intensity, and temperature on photo- 

 taxis. Vertical displacements were found to follow sudden 

 changes of light or of temperature. Galvanotropism, which 

 is very weak in Daphnia, was found to be quite strong in Gam- 

 marus, the specimens swimming to the negative pole. 



Following an account of the normal feeding reactions of 

 Stentor, Schaeffer " describes the results of several feeding 

 experiments to test the power of discrimination between dif- 

 ferent substances. Of the various materials swept into the 

 gullet of cilia, Stentor takes in only certain kinds. Others 

 are rejected by a quick reversal of the stroke of the cilia. The 

 organism discriminates more readily when nearly satiated with 

 food. When hungry it may ingest carmine and other indi- 

 gestible materials, and behave differently in several other 

 respects. Stentor apparently does not learn by experience 

 to improve its selection of food. Schaeffer repeated the ex- 

 periments of Metalnikow, on the basis of which it was claimed 

 that Paramoecium learns by experience to select its food more 

 advantageously, and obtained contrary results. No true learn- 

 ing was found in either of the species studied. 



The article by Simroth ^^ is devoted to the discussion of pre- 

 vious papers, and contains no new observations or theories 

 on this puzzling subject. 



