Literary Notices. 169 



sembling the infusoria in their mode of Ufe, in order to find whether 

 the reaction method of the metazoa differs radically in character from 

 that of infusoria. The following free-swimming Rotifera, which pro- 

 gress through the water in the same manner as the ciliate infusoria, 

 were studied; several species of the Rattulidae and of the Cathypna- 

 dae, two or three species of Euchlanis, Ploesoma lenticulare, Amiroea 

 cochkaris, and Brachionus pala. The stimuli used were chemicals^ 

 heat, light, and the constant electric current. The reactions of all 

 these Rotifera are essentially the same as those of the ciliate infusoria. 



Fourth Paper. The Theory of Tropisms. 



This paper forms an admirable summary and theoretical discus- 

 sion of the undoubtedly careful and exact observations described in 

 the foregoing three papers. And it is to be said, further, that in each 

 paper the author evinces the rare combination of qualities — a lively 

 theoretical interest combined with the power of impartial observation. 



The paper aims utterly to destroy the theory of the several 

 "-taxes." Firstly, the theory of Loeb and others that the direc- 

 tion of ray (in light and electricity) is the determining factor in orien- 

 entation is untenable, because all the organisms studied react only by 

 swerving toward a structurally defined side of their own bodies, even 

 although this movement causes them to turn directly toward the rays 

 that they seek to avoid. The theory that the intensity of stimulation 

 effects orientation by a local effect on such parts of the body as it 

 reaches is untenable, because in many, if indeed not most, organisms 

 the anterior end is the only part sensitive enough to be effected by the 

 stimuli (that is, the threshold of orientation is the threshold of stimula- 

 tion of the anterior end); and because, as in the previous case, the 

 response is invariably a perfectly definite "motor reaction" toward an 

 anatomically defined side of the body of the organism. The defend- 

 ers of the theory of tropisms will hardly call in question Professor 

 Jennings' patently exact and unbiased observations, nor his methods, 

 which are of the most careful, nor yet the range of organisms which 

 he has chosen to study, which is far greater than that of any other in- 

 dividual experimenter. But they may possibly ask Professor Jennings 

 what it is if not intensity of stimulation that causes the organisms, 

 while circling on their anterior ends as pivots, to dart forward more 

 or less suddenly at that point of the circle where the anterior end re- 

 ceives least of the undesirable stimulus ; and if this cause is the 

 intensity, whether his observations have not demonstrated a phototaxis 

 of the anterior end. But even if this were to be the case, Professor 

 Jennings would have effected a most important refinement on the old 



