Some evidence of intelligence seems to be displayed by the razor-fish. For the animals dislike salt, so that when this is sprinkled above their burrows in the sand, they come to the surface and quit their habitations. But if the animal is once seized when it comes to the surface and afterwards allowed to retire into its burrow, no amount of salt will force it again to come to the surface.[10] With regard to snails, L. Agassiz writes: 'Quiconque a eu l'occasion d'observer les amours des limaçons, ne saurait mettre en doute la séduction déployée dans les mouvements et les allures qui préparent et accomplissent le double embrassement de ces hermaphrodites.'[11] Again, Mr. Darwin's MS. quotes from Mr. W. White[12] a curious exhibition of intelligence in a snail, which does not seem to have admitted of mal-observation. This gentleman 'fixed a land-shell mouth uppermost in a chink of rock; in a short time the snail protruded itself to its utmost length, and, attaching its foot vertically above, tried to pull the shell out in a straight line. Not succeeding, it rested for a few minutes and then stretched out its body on the right side and pulled its utmost, but failed. Resting again, it protruded its foot on the left side, pulled with its full force, and freed the shell. This exertion of force in three directions, which seems so geometrically suitable, must have been intentional.' If it is objected that snail shells must frequently be liable to be impeded by obstacles, and therefore that this display of manoeuvring on the part of their occupants is to be regarded as a reflex, I may remark that here again we have one of those incessantly recurring cases where it is difficult to draw the line between intelligence and non-intelligence. For, granting that the action is to a certain extent mechanical, we must still recognise that the animal while executing it must have remembered each of the two directions in which it had pulled ineffectually before it began to pull in the third direction; and it is improbable that snail shells are so frequently caught in positions from which a pull in only one direction will release them, that natural selection would have developed a special instinct to try pulling successively in three directions at right angles to one another. The only other instance that I have met with of the apparent display of intelligence in snails is the remarkable one which Mr. Darwin gives in his 'Descent of Man,' on the authority of Mr. Lonsdale. Although the interpretation which is assigned to the fact seems to me to go beyond anything that we should have reason to expect of snail intelligence, I cannot ignore a fact which stands upon the observation of so good an authority, and shall therefore quote it in Mr. Darwin's words:--