158 G. H. PARKER 
of Ilyanassa with carmine suspended in seawater, not the least evi- 
dence of cilia could be discovered. I therefore believe that Ily- 
anassa moves by a form of muscular activity that does not appear 
as pedal waves and it is not improbable that other gastropods 
will be found that have the same peculiarity. That Vlés recog- 
nized something of this kind may be inferred from his statement 
that no changes in color can be seen in the creeping foot of Nassa, 
Buccinum, Aeolis, etc., and that the direction of the waves in 
these instances can be judged only by the deformations produced 
at the edge of the foot. As Vlés makes no further mention of 
Nassa in his subsequent account, I suspect that it is more or less 
like Ilyanassa and is capable of little or no pedal-wave movement. 
The locomotion of such gastropods I should designate as due to 
arhythmic pedal movements as contrasted with rhythmic pedal 
movements, such as have been fully classified by Vlés. 
It is a significant fact that all gastropods, irrespective of their 
type of movement (direct or retrograde), are restricted to 
forward locomotion. None, so far as I am aware, can reverse 
and move backward as, for instance, an earthworm can. What- 
ever differences these various types of pedal movements possess, 
they still lead to but one result, the forward locomotion of the 
snail. 
THE GASTROPOD FOOT AS A HOLDFAST 
The snail’s foot subserves the double function of attachment 
and locomotion. As means of attachment snails secrete a bed 
of mucus, and use the foot as a sucker. Both methods are com- 
monly employed by the same species, but in a given form one 
method is usually developed much in excess of the other. For 
instance, in Helix pomatia, Limax maximus, and other allied 
species, the moist surface of the expanded foot will stick with 
some tenacity to glass. But if such an animal be allowed to creep 
its length over a glass surface and thus spread a bed of mucus on 
which it can rest, it will be found to have multiplied the strength 
of its attachment many times. The mucus adheres to the glass 
and the surface of the foot to the mucus very much more power- 
