They have a great power of "homing" like pigeons, however far (for them) is their journey after favourite food. The slime-marked journeys or feeding tracks of this species (and still more of slugs) afford matter of great interest. As to sight the two eyes are the dark specks on the tip of the upper pair of "horns," but the range of vision is very short indeed, and the difference between light and approaching darkness is all that some seem able to perceive. The organs of hearing are two small sacs filled with fluid in which are some calcareous grains. They hear little which is audible to human ears, and if not altogether deaf they are dumb as far as we can hear. The power of taste they possess, as is shown by the preference of some foods to others. The sense of touch is acute and resides in all parts of the soft and moist external skin, and especially in the upper tentacles or horns in the _Helicidæ_. Jaws they have with which to seize and to bite off food, and in _H. aspersa_ and others these bear teeth, but the chief work is done by a sort of toothed tongue, the radula, which rasps off particles of food with a side to side motion of the head as the animal advances. Our _aspersa_ has 12,615 teeth on this ribbon, contained in 145 transverse rows. The organs of digestion are complex and practically much the same as our own. Little vegetation would be left in nature had not, on the one hand, snails been kept down by many enemies as well as by their need of hibernation and their short life; while on the other by numerous devices in the course of ages many plants have protected themselves against the moving machine of a snail's mouth. Cultivated plants, which generally lose their natural protections, have to be guarded by human guards or gardeners. Some plants defend themselves by prickles or hairs, some by hardening themselves with lime or flint, some by bitter or acrid juices. A heart of two chambers, veins, arteries, and blood our snail possesses, and, like man, the old snail has a slower pulse than the young one, and in both exercise increases the pulse rate and also warmth. Breathing is accomplished by a single chamber or air-cell, but also through the skin. As in the case of plants, some kinds are male and female separately, and as some have both powers and products in the same plant, so also is it with mollusca. _H. aspersa_ and most Gasteropoda are of the latter kind.