II STRENGTH OF SNAILS 45 



exactly in the same place), but it thinks better of it, and the 

 indeutatiou proceeds no further.^ According to Gundlach,^ 

 Helix imperator and H. crenilahris, two large species from Cuba, 

 possess the same property, which is said to be also character- 

 istic of the subgenus Stenopus (W. Indies). Amongst marine 

 species, Harpa ventricosa and Solen siliqua have been observed 

 to act in a similar way, Harpa apparently cutting off the end of 

 the foot by pressure of the shell. Karl Semper, in commenting 

 on the same property in species of Helicarion from the Philp- 

 pines (which whisk their tail up and down with almost convul- 

 sive rapidity, until it drops off), considers ^ it greatly to the 

 advantage of the mollusc, since any predacious bird which 

 attempted to seize it, but only secm-ed a fragment of tail, would 

 probably be discom-aged from a second attack, especially as the 

 Helicarion would meanwhile have had time to conceal itself 

 among the foliage. 



Strength and Muscular Force. — The muscular strength of 

 snails is surprisingly great. Sandford relates"' an experiment on 

 a Helix aspersa, weighing ^ oz. He found it could drag verti- 

 cally a weight of 2^ oz., or nine times its own weight. Another 

 snail, weighing -g- oz., was able to drag in a horizontal direction 

 along a smooth table twelve reels of cotton, a pair of scissors, a 

 screwdriver, a key, and a knife, weighing in all no less than 1 7 oz., 

 or more than fifty times its own weight. This latter experiment 

 was much the same as asking a man of 12 stone to pull a load 

 of over 3^ tons. 



If a snail be placed on a piece of glass and made to crawl, it 

 will be seen that a series of waves appear to pursue one another 

 along the under siu-face of the foot, travelling from back to 

 front in the direction in which the animal is moving. Simroth 

 has shown that the sole of the foot is covered with a dense net- 

 work of 'muscular fibres, those which run longitudinally being 

 chiefly instrumental in producing the undulatory motion. By 

 means of these muscles the sole is first elongated in front, and 

 then shortened behind to an equal extent. Thus a snail slides, 

 not on the ground, but on its own mucus, which it deposits 

 mechanically, and which serves the purpose of lubricating the 



^ Riiymoud, Nautilus, iv. p. 6. 

 - Quoted by Oehlert, E^v. Sc. xx.\viii. p. 701. 

 ^ Aniinal Life, Intern. Scientif. Scr. ed. 1, p. 395. ■* Zoologist, 188(5, p. 491. 



