38 THE CHICAGO ACADEMY OF SCIENCES. 



TABLE VII. 

 Intervals between the breathing spells of Lymnceus palustris. 



'The amount of atmopsheric air taken in by any individual dur- 

 ing 24: hours depends not so much on the number of times it opens its 

 respiratory tube at the surface as upon the length of time the tube re- 

 mains open for inhalation. In this particular the 12 snails under obser- 

 vation exhibited decided individuality, some keeping the tube open only 

 a fraction of a second, while others extended the period of inhalation 

 even to 96 seconds. No. 4, Table VII, whose average interval was 16 

 seconds, kept the respiratory tube open noticeably longer than any 

 other snail 40 and 50 seconds being its usual length of time, and 96 

 seconds the limit, while the average time of inhalation for the other 

 snails was about 15 seconds." 



Many Lymnseas have been observed to breathe without coming to 

 the surface, and such respiration is considered abnormal. Pauly di- 

 vides these abnormal breathers into three classes, as follows: 



1. Abyssal snails which cannot possibly reach the surface. 



2. Snails which make no attempt to reach the air though living 

 in shallow water. 



3. Snails artificially restrained from securing atmospheric air. 



The first class has already been discussed (see under bathymet- 

 rical range). Pauly cites a number of examples in which the animals 

 secured air without visiting the surface of the water, and he explains 

 as the reason for this change of habit, the ability of the snails to se- 



