208 G. H. PARKER 



that divers who are collecting strombs are said often to be cut 

 on the breast by these conchs when, with an armful held tightly 

 to the body, the diver is swimming to the surface. Strombus, 

 then, attaches its foot by pressing the two ends of that organ 

 vigorously against the substrate and by relying more or less 

 upon the weight of the shell to hold the foot in place while the 

 shell itself is being thrown forward. 



The weight of the shell is considerable and no one can watch 

 the locomotion of Strombus without being impressed by its 

 strength. In an immature specimen whose living body weighed 

 49 grams the shell weighed 173 grams, making a total of 222 

 grams, yet the relatively small amount of musculature in this 

 animal was sufficient to enable it to make considerable leaps 

 even in the air. In the sea-water the shell is, of course, relatively 

 lighter, and in consequence the animal can leap rather farther 

 than in air. The shell that weighed 173 grams in the air, weighed 

 only 105 grams in sea-water, the whole animal, shell and soft 

 parts, weighing 110 grams in water as against 222 grams in air. 

 Thus in its more usual habitat, in sea-water, the stromb has less 

 work to do in moving its shell than it has in air, but such 

 work even when the animal is in the water is by no means 

 inconsiderable. 



Thus the locomotion of Strombus is accomplished by means 

 radically different from those used by other gastropods, for the 

 muscular action involved in the leap of this snail is in no obvious 

 way related to the muscular waves that pass over the foot of 

 most moving gastropods and is absolutely distinct from ciliary 

 activity which, contrary to my former view (Parker, '11, p. 157), 

 has been recently shown by Copeland ('19) to be the means of 

 locomotion in several gastropods. 



SUMMARY 



Pedal locomotion in gastropods is accomplished either by 

 gliding (an operation dependent upon muscular waves passing 

 over the foot or by ciliary action) or, in Strombus, by leaping, 

 an act that involves the forward extension of the foot, its fixa- 

 tion in the substrate by its anterior and posterior ends, and a 



