MOLLUSCA THEIR DISEASES. 379 



very boldest of his statements, — the renewal of the entire 

 head, — has been even established by naturalists in the fullest 

 manner, for it is not true, as Bosc and others would have 

 us to believe, that " the animal infallibly dies when the 

 first ganglion, which essentially constitutes the head, has 

 been taken away." * In 1808, M. Tarenne decapitated 

 many snails, and proved, by careful dissection, that the am- 

 putated portion contained not only the tentacula, the jaw, 

 and the upper lip, but the brain likewise, and the anterior 

 part of the foot, yet these maimed individuals reproduced 

 the head complete at the end of one year or more. The 

 new head only differs from the old by having a paler and 

 smoother skin ; and sometimes a sort of furrow marked its 

 junction with the trunk. f 



It is not, as Spallanzani ascertained, every kind of snail 

 (Helix), which possesses the power in question ; nor is the 

 power limited to that family of Mollusks. From a very 

 early date in the history of animals, it has been affirmed 

 that the Cuttle-fish could renew their amputated limbs ; 

 and the snail of the beautiful Harp-shells (Harpa) repro- 

 duces its foot. This member is so disproportionably large 

 that it cannot be drawn within the shell in extraordinary 

 circumstances, so that when attacked by an enemy the Mol- 

 lusk, by pressing the foot firmly against the sharp lip of the 

 shell, voluntarily cuts away the hinder portion, and thus 

 secures its safety by the loss of its limb. J In two or three 

 species of pectinibranchial zoophagous Mollusca Madame 

 Power proved the reproductive agency in them by direct 

 experiment. She lopt off the tentaculum with the eye 

 from a Triton nodiferum, and at the end of twenty days 

 a new tentaculum had grown six lines in length, — " that 

 which had been cut off measured fourteen lines." A Murex 

 trunculus reproduced the head and tentacula, and the oper- 

 culum, which had been purposely torn away ; and a Conus 

 its tentacula and respiratory siphon. § The foot of the 

 Mussel (Mytilus edulis) being cut off will be renewed. 



The diseases of the Mollusca are scarcely known ; and all 

 the accurate information we possess is limited to their para- 

 sites. Of terrestrial Mollusca, Reaumur has described in 

 detail a sort of mite which infests the Helicidae or Snails 

 of France. It is found in numbers on them in dry weather, 

 but rarely in rainy seasons, for the viscid secretion of the 

 snail being then abundant seems to destroy the parasites. 



* Gritlith's Cuvier, part xxxix. p. 329. Bosc. Vers. i. 80. 



t Bowdich's Man. of Conchology, i. 7~>. 



X Hang's Manual, p. 211. § Charlesworth's Mag. N. Hist. ii. 64. 



