BY F. ROLAND HAYES, B. SC. 159 



II. Experimental Technique 



For the experiments in negative geotropism cylindrical 

 glass jars were used, 45 centimeters high and possessing an 

 inside diameter of 6 centimeters. These jars were so graduated 

 that the distance that an animal had travelled from the bottom 

 at the time a reading was taken, could be accurately determined. 

 In most experiments four such jars were used, two of them filled 

 to within 5 centimeters of the top with oxygenated sea water, 

 and two freshly rinsed out with sea water in order to dampen 

 the inside and reduce the temperature. 



Five individuals were placed in each jar and their progress 

 upwards on the inside wall of the jar recorded every ten minutes. 

 Thus the experimental result for each "immersed" and "dry" 

 jar experiment is usually computed from the average perfor- 

 mance of 10 individuals, never from less than five. As soon as 

 any animals reached the surface of the water further readings 

 were considered invalid and have been disregarded as far as 

 possible in calculating results. 



All calculations have been made with reference to a single 

 periodical reading which has been carefully selected as the most 

 typical of the series. In general the procedure has been to use 

 the first reading recorded after any individual had reached the 

 top of the jar. This usually has been the 20 minute reading. 

 The height to which each "immersed" and each "dry" animal 

 had climbed, was noted, and the total distance that all the 

 animals of each group had ascended was found. This was 

 divided so that a figure was obtained which represented the 

 average performance per individual per 10 minutes in centi- 

 meters, and this is the experimental result quoted. 



It will be observed that no opportunity was offered by 

 this experimental technique for the animals to exhibit positive 

 geotropism. In view of preliminary experiments which were in 

 complete harmony with the results of Kanda (1916-2), who show- 

 ed that on a vertical surface 100 per cent oiL.littorea exhibit 

 negative geotropism, this precaution was not deemed necessary. 



