82 William B. Herms 



lamp from one side of the tube to the other resulted likewise. 

 Gradually increasing the distance between the vial and the light 

 resulted in a return to the food when a maximum of thirteen feet 

 was reached. On decreasing the distance again, the larvae once 

 more left the food when a distance of nine feet was reached. This 

 experiment was repeated several times with like results. 



The lamp used was an ordinary oil lamp with small (No. l) 

 wick turned up fairly well. The adjustment to what was appar- 

 ently the exact point of greatest photic stimulation w^as very 

 remarkable, as was the almost frantic effort to gain this point when 

 the angle was changed. Here we have an example of positive 

 phototaxis overcoming the action of positive chemotaxis which is 

 surely not a useful reaction. 



Stereotaxis 



The larvae when placed in a receptacle which was ridged, preferred 

 to crawl in the grooves. In one instance larvae were kept in a 

 bottle which had a convex bottom; on examination later, all were 

 found in a circle wedged in close together around the margin of 

 the bottom, with heads down and posteriors extended. On 

 several occasions larvae were found crawling in the crevices of the 

 floor, and some of these were wedged in so tightly that it was a 

 task to extricate them without injury to the larvae. 



Positive stereotaxis is a prevailing phenomenon in the lower 

 orders and fly larvae are no exception. 



Geotaxis 



Fly larvae are positively geotactic, the burrowing habit ( ^) being 

 very marked. On the other hand, imagines when first emerging 

 from the pupa cases crawl out of the sand and up nearby grasses, 

 remaining there until the wings are spread and dry. The cut 

 showing this also illustrates how the flies cling to the grasses with 

 head dow^nward. 



Note — The experiments and observations relating to this paper were conducted at the Ohio State 

 University Lake Laboratory at Sandusky, Ohio, chiefly during nine weeks of the summer, 1905, and a 

 portion of the summers, 1903 and 1904. 



The writer is indebted to Prof. Herbert Osborn, Director of the Lake Laboratory and Asso- 

 ciates. Profs. F. L. Landacre and J. S. Hine; also to Dr. W. E. Kellicott, Barnard College, for the 

 kind assistance rendered and suggestions offered during the course of these studies. 



