LYMNZID4 OF NORTH AMERICA. 35 
in those regions between the parts of the foot that are fixed to the 
substratum serves to advance the animal. 
“The presence of cilia on the surface of the foot has been re- 
peatedly demonstrated. These cilia may be easily seen on young snails 
by means of the microscope. In this connection it is interesting to 
note that a young Physa primeana, ten days old, showed cilia in motion 
not only around the edge of the foot, but over the tentacles as well.” 
RATE OF LOcomMoTION. The Lymnezas are usually sluggish crea- 
tures, content to browse slowly over the surface or to remain hunched 
at or above the surface of the water. Mr. Walter (1. c., p. 13) has 
experimented with Lymnza with the following result: 
Number of 
seconds required Number of 
to go 1 inch. trials. 
70° 60 
78 80 
141 25 
220 30 
The average time was found to be 106 seconds. 
d. RESPIRATION. 
Respiration in Lymnza is carried on normally by means of a so- 
called lung, which is a fold of the mantle occupying the last part of 
the body whorl. This forms a sac or cavity into which the air¢ is 
taken through a modified portion of the mantle which forms a tube 
or siphon. This cavity is well supplied with blood vessels, the air 
taken into the lung eriating the blood in these veins before it enters 
the heart, after it has circulated through the body. 
To obtain the air for respiratory purposes, Lymnza visits the 
surface of the water periodically. When the surface is reached, the 
body is swung around to the right and the siphon opens above the 
surface with a distinct clicking sound. Apparently the snail is not 
aware that the surface has been reached until the tip of one, or both 
tentacles are in contact with the surface film, at which instant the 
siphon is brought into position. This peculiarity has been observed 
in a number of species of Lymnza and is mentioned by Walter and 
others. The individual, after filling the respiratory chamber with air, 
1The following experiment by Walter is of interest: 
“To demonstrate that the rate of progress of a single snail changes when 
the latter is forced to make repeated attempts to reach the surface, a single 
instance, which is typical of the behavior of all the snails that were subjected 
to experiment, is given. In the 60 trials of Lymnaeus the escape from the 
two-inch circle for the first 20 trials took, on the average, 45 seconds. The 
second 20 trials averaged 63 seconds, while the average for the last 20 trials 
was 101 seconds. This slowing down may have been simply the effect of 
Baste ue but more likely it was due to the gradual exhaustion of the mucus 
supply.” 
