218 WILLIAM BRODBECK HERMS 



at every point opportunity for development, and shows even in 

 the unicelhilar organisms what must he considered the beginnings 

 of intelhgence and of many other quaUties in higher animals." 



The third theory (the method hy randorn movements)is that of 

 Holmes and is, as its author suggests (Holmes, '05a, p. 106), 

 "sL form of the trial-and-error method minus the element of 

 learning by experience." it is also regarded as ''more indirect." 

 Its definition (p. 102) is briefly as follows. "Of a number of ran- 

 dom movements in all directions only those are followed up which 

 bring the animal out of the undesirable situation." 



How well this latter method of orientation fits the case may 

 be seen by an examination of figs. 16 to 25. Not less may be said 

 of the second method, indeed, as has already been maintained by 

 the writer (Herms '07, pp. 80-81), there is so little difference be- 

 tween the two methods in their application to fly-larvae, that they 

 might be regarded as equally applicable were it not for the 

 qualifying statement of Holmes ''minus the element of learning 

 by experience." There seems little ground for coubting that either 

 the second or third methods find their application in the behavior 

 of these organisms under the given intensities (figs. 16, 17, 20, 21, 

 22, and 25) ; but increasing the intensity lessens very decidedly 

 the number of random movements, as illustrated by figs. 18, 19, 

 and 23. This result is in accordance with the statement of Loeb ('88, 

 p. 3) that the orientation of the animal in the direction of the 

 rays is more precise as the intensity increases. It was also found 

 by Harper ('05, p. 17) in the earthworm (Perichaeta bermudensis) 

 that "random movements are a feature of less strong light, tend- 

 ing to disappear with the increase of intensity, and are replaced by 

 direct orientation in very strong light." 



To test the influence of a range of intensities on the production 

 of random movements, the larvae were started in a very low direc- 

 tive intensity (0.5 to 1.0 CM.), and after the individuals had 

 oriented and were crawling away, the directive light was turned 

 off leaving the larvae to creep in total darkness for 15 to 20 seconds, 

 when a new directive light from in front of the animals was sud- 

 denly turned on. It may be seen by the courses illustrated in 

 figs. 16 to 23, that sudden darkness had no apparent effect on the 



