20 Journal of Cojnparativc Neurology and Psychology. 



others give no evidence of perception of the height until they 

 have reached the edge, it was necessary to make the record as 

 described. Since in these experiments it was necessary that 

 time as well as space should be considered, 60 minutes was fixed 

 as the duration of the experiment, and in case the animal re- 

 mained on the board longer than that period the test was re- 

 corded as a failure. Failures in this case have positive value, 

 to be sure, but they do not give us the accurate measurement 

 of the time of reaction which indefinite prolongation of the 

 period of observation would furnish. 



For detailed study three species were chosen : Chrysemys 

 picta Schneider, as a representative of the water inhabiting 

 forms ; Na^tejnys guttata Schneider, to represent those species 

 which spend part of their lives in water and part on land, and 

 Terrapene Carolina Linnaeus, as a strictly land inhabiting form. 



Several individuals of each of the species were studied. 



In the tables the results for four individuals of each are pre 



sented. Each individual was given one trial a day at each of 



the three heights, 30, 90 and 180 cm. for ten days. In Table 



I we have a summary of the results, which are given in detail 



for the various individuals in Table II. From an examination 



of the records the following facts appear: (i) The time spent 



on the board is shortest for the water species, longest for the 



land species. This indicates that the hesitation in the presence 



of a void increases as we pass from the strictly water forms to 



TABLE I. 



Reactions to Spatial Conditions of Tortoises of DiiTerent Habits. 

 Summary of Results. 



