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 Lymnza to live for great lengths of time without 
air has been noted by many conchologists. As has already been stated, 
Lymnea 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 Lymnza regarding their respiration, among others 
Mr. A. Pauly* 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 Lymnezas 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 Lymnzas for a considerable period after 
being hatched (about ten days). Where bubbles of air are present, as 
in shallow water containing air plants, Lymnza has been noted to use 
them for obtaining air, thus obviating the necessity for coming to the 
surface. Forel and Brot, while investigating Lymnea 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', Siebold, Clessin and others believe that in some cases 
Lymneza 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? that Lymnza normally re- 
spires water and only comes to the air when compelled to do so by an 
unusually high temperature. Walter? has conducted some very sug- 
gestive and interesting experiments on the breathing habits of Lym- 
nza, 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. 
sai PAY edad der Mat. Phys. Classe der K. Bayer. Akad. der Wissen., 1875, 
?Mal. Blatt., XXIV, p. 175. 
3Cold Spring Harbor Mon., VI., p. 14. 
4Uber die Wasserathruna der Limnaeiden, 1877. 
