II STRENGTH OF SNAILS 45 



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

 proceeds no further.^ According to Gundlach,^ Helix imj^erator 

 and H. crenilahrls^ two large species from Cuba, possess the 

 same property, which is said to be also characteristic of the sub- 

 genus Stenopus (W. Indies). Amongst marine species, Harpa 

 ventrieosa and Solen sillqua have been observed to act in a simi- 

 lar 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 Helieario7i from the Philippines 

 (Avhich whisk their tail up and down with almost convulsive 

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

 tage of the mollusc, since any predacious bird which attempted 

 to seize it, but only secured a fragment of tail, would probably 

 be discouraged 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 21 oz., or nine times its own weight. Another 

 snail, weighing -^ 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 17 

 oz., or more than fifty times its own weight. This latter ex- 

 periment 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 surface 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 



1 Raymond, Nautilus, iv. p. 6. 



2 Quoted by Oehlert, Bev. Sc. xxxviii. p. 701. 



3 A7umal Life, Intern. Scientif. Ser. ed, 1, p. 395. •* Zoologist, 1886, p. 491. 



