The Problem of Orientation 71 



one that is of general applicability to the directed 

 reactions of lower and higher Metazoa?" 



"In considering the evidence on this question, we 

 find that even in the symmetrical Metazoa the di- 

 rection of movement with reference to external 

 agents is by no means always brought about by a 

 simple, direct turning. On the contrary, in many 

 of the Metazoa, trial movements are as noticeable 

 and important as in the Protozoa. This we have 

 illustrated in detail for many invertebrates in the 

 section devoted to this subject (Chapter XII, Sec- 

 tion 2 ) . For such behavior the local action theory 

 of tropisms fails to give determining facts." 



Just how Jennings would explain orientation such 

 as occurs when the moth flies into the candle he 

 has nowhere made clear, further than saying that 

 in such cases the organism "reacts as a whole," in- 

 stead of being oriented by the local reactions of par- 

 ticular organs. 



That the orientation of a symmetrical organism 

 may be largely brought about by the indirect method 

 of a sort of trial and error process has been shown, 

 in the case of several organisms, by the present 

 writer. In a paper on the "Selection of Random 

 Movements as a Factor in Phototaxis" I have shown 

 that in earthworms, leeches (Glossiphonia), and the 

 larvs of blow flies, there is a fairly definite orien- 

 tation of the body to light rays as the animals move 

 away from the source of illumination, and that it 

 is not so much through a direct turning away from 



