94 VICTOR E. SHELFORD. 



Furthermore these toads are probably physiologically dif- 

 ferent from toads of moister situations. The toads are the 

 only sand animals used that clearly avoided dry air. The 

 stimulation was less marked than that of the wood frogs and 

 was not accompanied by striking or characteristic reflexes. 

 Activity was greater in the controls of gradient experiments 

 where uniform current was used than where still air was used 

 (Chart II., Expt. 23, p. 90). In the gradient the toads were 

 negative to drier air (Table III.) but turned back much less defi- 

 nitely than did the salamanders. Rapid random movements 

 appeared to be characteristic. The ability to orient in the 

 gradient is poorly developed. 



The spiders (Geolycosa) appeared not to be affected by the moist 

 air. When observed in the tubes, no differences between the 

 individuals in the different conditions could be noted. In the 

 gradient experiments (Table II.) a positive reaction to dry air 

 was clearly shown when the spiders were induced to move about. 

 It was necessary to select individuals of the same sex and of 

 about the same size, as these animals manifested a very striking 

 repulsion for one another and when one spider came near to 

 another one or both darted away with great speed. Thus when 

 one spider moved, three being present, more movement usually 

 resulted and if none of the spiders was killed in combat the 

 experiment resulted successfully. In many cases however, espe- 

 cially when differences in size or sex occurred, some of the 

 spiders usually were killed before the experiment ended. Experi- 

 ment 29, Chart IV., shows a typical graph characterized by the 

 erratic dashes made by two individuals when meeting. 



The digger wasps (Microbembex') were likewise slightly posi- 

 tive (Table II.) to dry air, though their chief reaction was dig- 

 ging (Chart V., p. 97). The digging reaction took place in the 

 medium and moist air but not in the dry. There was no special 

 activity in the dry air. In Chart V. the reaction of three indi- 

 viduals in a gradient is shown; the crosses indicate that the 

 wasp was digging at the half minute opposite which the cross 

 appears. It will be noted that the crosses are all in the moist 

 and medium sections. 



A few experiments were tried with grasshoppers from sand 



