38 VICTOR E. SHELFORD 



which is, I believe, the difference between a graph in which modi- 

 fication of at least one individual is indicated and one in which 

 there is little or no evidence of modification. In Expt. 73, 

 clearly one individual tried air of highest power, then turned 

 back with the second trial, and repeated the same after a brief 

 stay in the moist air. The others appear to have avoided the 

 middle section except for one trial of the air of high evaporating 

 power, after which all came to rest in the moist air. The control 

 of 73, when compared with the rest of the controls indicates the 

 greater activity which commonly occurs in the air that is moving 

 enough to raise the evaporation above the optimum for the 

 animals. 



Evidence of modification, as in the case of the fishes (Shelf or d 

 and Allee, '14), may be of the following types: (a) an animal 

 may begin turning back after entering the stimulating air a number 

 of times, (b) it may spend shorter and shorter periods of time in 

 the modified air with each entrance; (c) after entering the grad- 

 ient and turning back in it, an animal may begin to turn back 

 before the change of air conditions is encountered, indicating 

 retention; (d) after having experienced differences in one tank 

 it may remain in one end and turn back from the other when 

 there is no difference between the two ends. The second two 

 types of modification may indicate learning while the first two 

 do not. 



Table 1 gives the data on these questions by species and factors. 

 The kinds of experiments in which there was no evidence of modi- 

 fication, are omitted. For example, the experiments with Fon- 

 taria and wind gave no good evidence of modification and 

 only experiments with reactions to dry and heated air are included. 



Where the reactions were strongly negative the animals some- 

 times turned back the first time they encountered the stimulating 

 air (Chart I, Expt. 71; Chart III, Expt. 73). All of the species, 

 except Pterostichus which was used for only one experiment, 

 did this when the. evaporation was great. Such turnings indicate 

 that the animals sense the strong stimulii the first time they en- 

 counter them, i.e., before their sensibility has been increased by 

 repeated contacts with the stimulating air. We note the figures 

 showing the number of times this happened, in the twelfth 

 column of the table. Usually the animals showing modification 

 entered the stimulating air a number of times before beginning 



