340 \V. vox BUDDENBROCK 



animal differ according to the direction from which the attract- 

 ing force comes. Prentiss 5 and I 6 have further shown that the 

 loss of the statoliths alone has the same effect as the loss of 

 the whole organ. 7 



There is here absolutely no such action of energy on the living 

 tissue as the tropism theory requires; the energy acts upon the 

 lifeless statoliths, and the whole phenomenon belongs in the 

 category of mechanical stimuli, and consequently is excluded 

 from Loeb's scheme. 



Other phenomena that are often cited as tropic movements 

 that take place without the conditions assumed as necessary by 

 Loeb, but which are normal in other respects, are the clearly 

 denned avoiding reactions which infusoria exhibit toward harm- 

 ful stimuli. When a number of these animals, for example, 

 Paramoccium or Stylonych a, are placed under a cover glass the 

 phenomena of chemo- and thermotropism may be readily studied, 

 as many textbooks state, and in. green species heliotropism is 

 often manifested. 



But since these animals are entirely asymmetrical in struc- 

 ture, the tropism theory is not applicable to them, because it 

 presupposes two symmetrical body halves or a radial plan; 

 so that these may be cited as further examples in which tro- 

 pisms occur without fulfilment of the required conditions. The 

 method, however, by which the infusoria avoid the harmful 

 stimuli is not a swimming in a straight line away from the 

 source of energy, but the making of so-called trial movements. 

 These are. therefore, not true tropisms, as I would emphasize 

 in agreement with Loeb against Jennings, so that these cases, 

 like most trial movements, cannot well be used in criticism of 

 Loeb's theory. 



5 Prentiss, C. W. The otocyst of decapod Crustacea. Bull. Mus. Comp. Zool., 

 Harvard, Vol. 36, 1901. 



G v. Buddenbrock, W. Ueber die Orientierung der Krebse im Raum. Zool. 

 Jahrb., Abt. /. allg. Zool. u. Physiol., Rd. 34, 1914. 



7 According to E. P. Lyon the case is different in certain fishes, since here, when 

 the statoliths are carefully removed without injuring the sensory epithelium, no 

 resultant loss of function is observed. The accuracy of this observation seems 

 doubtful to me, because blood clots, which are almost unavoidable in the statocyst 

 cup, apparently may assume the role of the statoliths. For our present discus- 

 sion, however, the fish behavior is immaterial, since we have only to show in this 

 case that certain geotropisms, not all, belong in the category of mechanical stimuli. 



