1S4 



E. H. HARPER 



PLATE 



A B B B 



A «- 



t V V 



F-3 1 



Aqqr\ 



Surface of n,0 



SJrS Aggregation 



B C B C B 





PLATE 2. 



F.ql 



!f^ -■;■■ 



^i't'ii','. 





£ _J 



r; s .2 



Fiq . 3 



Plate I. Figures 1, 2, 3, refer to experiments in the text of the same Dumber. 



The arrows indicate the oriented movements upward, downward, and toward 

 the magnet. 



Random movements of dispersal from the top of the upward stream, and at all 

 other points, are not represented. 



A, upward oriented movements in the region of increased buoyancy. 



B, heavily loaded animals moving downward in the weaker magnetic field. 



(', upward oriented animals consisting presumably of those which are less heavily 

 loaded. These tend to form the aggregation at the top which appears in (2) and 

 (3), but not in (1). 



D, horizontal paths of animals very close to the water surface or to the bottom, 

 which appear to be governed by nearness to these surfaces. 



E, individuals lying quiescent on the bottom, drawn passively at first toward 

 the magnet. 



The small curved arrows represent paths toward the magnet. The animals 

 swing gradually into the upward stream. The arrows are curved to indicate this 

 fact. Plate 2 illustrates t he same facts by another method. 



