8O II \S. \V. HAKC.II I . 



these locomotor movements take place usually during the night. 

 This I have demonstrated by carefully marking ldc.it ions and 

 noting subsequent changes. At no time have 1 found evidence 

 of these movements during the day. 



In general my experiments proceeded along the lines employed 

 by Loeb ('90, Arch.f. ges. Physiol., Bd. 47, p. 391), who>c objec- 

 tive aim was to establish the essential identity of heliotropism in 

 animals and plants, and his experiments were directed to that. 

 end. Incidentally it may be observed that he does hot hesitate 

 to claim "I think I have shown that the heliotropism of sessile 

 animals is essentially identical with the heliotropism of sessile 

 plants." And still later he asserts even more strongly, "It was 

 possible to show that heliotropism of animals agree in every point 

 with that of plants" ("Comp. Phys. of Brain," 1900, p. 181). 

 It may be doubted whether, in the light of present knowledge, 

 this would be seriously maintained. I shall not discuss the mat- 

 ter here further than to say that my own experiments were 

 undertaken with a very different aim, namely, that of ascertaining 

 the questions of fact, Are these organisms heliotropic? and 

 further, Do they exemplify, or conform to the mechanical concept 

 of behavior? 



In the following account I shall present the matter under some 

 three distinct series. First, those experiments made in tin 

 aquaria located in a north room; second, those conducted in the 

 smaller- experimental aquaria; and third, those conducted in the 

 large aquarium located in a room with exposure to direct sunlight. 



The first series began on January 6 with some six specimens. 

 To these additions were made from day to day, till on the i^th 

 I had twenty, which had been variously distributed in the two 

 large aquaria, some with the- heads directed away from the win- 

 dows, others directed at right angles, and still others facing the 

 windows. The aquaria were ol about the same si/e, probably 1.5 

 meters in length, by about 40 cm. in depth and width; the one 

 with its end toward the- window, the other with its side toward 

 the light. It was some time after specimens had become at- 

 tached before any sign of orientation was discernible. In the 

 aquarium (\o. II with the end directed louard the light there 

 were twelve specimens, in the other eight. The twelve had 



