REACTIONS OF ANIMALS. 93 



until death ensued. Inactivity or very slow movements were 

 characteristic of the second, third and fourth half-hour periods. 

 Marked reduction in size was evident in about two hours. They 

 died after two and one half hours. 



Comparable results were obtained with several snails. Polygyra 

 thyroides Say, when active at the time put into the observation 

 tubes, behaved as follows. In the moist air activity continued 

 intermittently. The animals retreated into the shell from time 

 to time and usually remained stuck to the side of the tube for 

 half an hour or more. In the dry air withdrawal into the shell 

 followed in five minutes but partial extension sometimes con- 

 tinued from time to time during the first half hour. In one 

 individual, a fresh epiphragm was formed at the end of two hours 

 and shrinkage and withdrawal into the shell continued during 

 several hours of observation. Polygyra palliata Say behaved 

 similarly. Active individuals put into dry air became inactive 

 but more quickly than thyroides. When put into the tubes in an 

 inactive state and with strong epiphragms no activity occurred 

 in either medium or dry air. In the moist air the foot was pro- 

 truded after 45 to 55 minutes and creeping began after 70 minutes. 



On one occasion specimens of several species were taken from 

 the same stock jar and placed in the moist air together, with the 

 following results: Polygyra palliata Say and P. thyroides Say 

 became active in 10 to 20 minutes, Pyramidula alternata Say 

 in 80 minutes, Polygyra fraudulenta Pit. showed no activity at 

 the end of three hours and forty minutes but was found moving 

 14 hours later, a night having intervened. The experiments 

 were carried far enough to show that activity may ordinarily 

 be induced in faint light by air nearly saturated with moisture 

 but it is clear that other factors are concerned because occa- 

 sionally it is not induced and when so, frequently does not 

 continue. 



(&) Sand Dune Animals. 



Of the sand area animals studied, the common toad is least 

 characteristic of sandy situations because toads belonging to thfe 

 same species are found in moist woods, and because toads 

 of the dunes breed in the pools and not on the dunes. 



