Braun took young individuals of _Limnaea auricularia_ on the day they were hatched out, and placed them singly in separate vessels with differing amounts of water. This was on 15th June 1887. In August 1888 specimen _A_ had only produced a little spawn, out of which three young were hatched; specimen _B_ had produced four pieces of spawn of different sizes, all of which were hatched; specimen _C_, which happened to be living with three _Planorbis_, produced five pieces of spawn distinctly Limnaeidan, but nothing is recorded of their hatching. Self-impregnation, therefore, with a fruitful result, appears established for this species of _Limnaea_.[97] =Reproduction of Lost Parts.=--When deprived of their tentacles, eyes, or portions of the foot, Mollusca do not seem to suffer severely, and generally reproduce the lost parts in a short time. If, however, one of the ganglia is injured, they perish. Certain of the Mollusca possess the curious property of being able to amputate certain parts at will. When _Prophysaon_, a species of Californian slug, is annoyed by being handled, an indented line appears at a point about two-thirds of the length from the head, the line deepens, and eventually the tail is shaken completely off. Sometimes the _Prophysaon_ only threatens this spontaneous dismemberment; this line appears (always exactly in the same place), but it thinks better of it, and the indentation proceeds no further.[98] According to Gundlach,[99] _Helix imperator_ and _H. crenilabris_, 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 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 Philippines (which whisk their tail up and down with almost convulsive rapidity, until it drops off), considers[100] it greatly to the advantage 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[101] an experiment on a _Helix aspersa_, weighing ¼ oz. He found it could drag vertically a weight of 2¼ oz., or nine times its own weight. Another snail, weighing ⅓ 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 experiment was much the same as asking a man of 12 stone to pull a load of over 3¾ tons.