36 THE CHICAGO ACADEMY OF SCIENCES. 



closes and draws the siphon from the air and turns about, usually in 

 search of food. 



The power of Lymnaea to live for great lengths of time without 

 air has been noted by many conchologists. As has already been stated, 

 Lymnaea and other fresh-water pulmonates normally come to the sur- 

 face at more or less regular intervals to obtain a fresh supply of air 

 for the respiratory cavity. It has been noted that visits to the sur- 

 face are more frequent in water which is poor in oxygen than in water 

 in which the normal amount is present. Several zoologists have made 

 experiments with Lymnaea regarding their respiration, among others 

 Mr. A. Pauly 4 who noted that the animals came to the surface for air 

 at intervals varying from a few minutes to several hours. In no case 

 did he find that water was allowed to enter the respiratory cavity, even 

 in individuals which were kept from air for ninety days, in which case 

 respiration was accomplished by the skin and not by the lung. It is 

 suggested by Pauly that those Lymnaeas living at great depths in lakes 

 may retain the primitive use of the lung to respire air from the water, 

 as is the case with all young Lymnaeas for a considerable period after 

 being hatched (about ten days). Where bubbles of air are present, as 

 in shallow water containing air plants, Lymnaea has been noted to use 

 them for obtaining air, thus obviating the necessity for coming to the 

 surface. Forel and Brot, while investigating Lymn&a abyssicola, found 

 that the pulmonary chamber of this species contained no air at the 

 moment it was taken from the water, but when placed in a jar it im- 

 mediately fell into the habits of its shallow-water relatives, coming to 

 the surface for air and also passing considerable periods out of water. 



Forel 1 , Siebold, Clessin and others believe that in some cases 

 Lymnaea breathes directly from water introduced into the respiratory 

 cavity, if compelled to remain away from the air for any great length 

 of time. Clessin expresses his opinion 2 that Lymnaea normally re- 

 spires water and only comes to the air when compelled to do so by an 

 unusually high temperature. Walter 3 has conducted some very sug- 

 gestive and interesting experiments on the breathing habits of Lym- 

 naea, the results of which seem of enough importance to reproduce. 



"Pauly states that the intervals between atmospheric breathing 

 are directly dependent upon the course over which the snail travels to 

 reach the surface, and he supports this conclusion with a table giving 

 sixteen observations on four snails. 



'Sitzungs. der Mat. Phys. Classe der K. Bayer. Akad. der Wissen., 1875, 

 pp. 39-54. 



*Mal. Blatt., XXIV, p. 175. 



3 Cold Spring Harbor Mon., VI., p. 14. 



Uber die Wasserathruna der Limnaeiden, 1877. 



