12. This is the nature of the malacia. They say that ... form their rough shells round themselves like a hard breastplate, which increases as they grow, and that they can leave these, as if they were a hole or a habitation. The nautilus is a polypus peculiar both in its nature and its actions; for it sails upon the surface of the sea, rising up from the depths of the waters. It is brought to the surface with its shell inverted, in order that it may go out more easily and navigate in an empty shell. When it reaches the surface, it turns its shell over. There is a membrane extended between two of its tentacula similar to the web feet of birds, except that theirs is thick and that of the nautilus thin and like a spider's web. This it uses for a sail when the wind blows, and it extends two of its tentacula for rudders. If alarmed, it fills its shell and sinks in the sea. No one has made any accurate observation on the production and growth of the shell. It appears not to originate in sexual intercourse, but to be produced like that of other conchylia, nor is it clear whether it can live when taken out of its shell. CHAPTER XXVI. 1. The most laborious of all insects, if compared with the rest, are the tribes of ants and bees, with the hornets, wasps, and their other congeners. Some of the spiders are more neat, graceful, and skilful than others in their mode of life. Every one may see the diligence of the ant; for it is on the surface, and that they always travel in one direction, and make a store and treasure-house of food, for they work even in the night when there is a full moon. 2. There are many kinds of spiders and phalangia. Of the phalangia that bite there are two sorts. The one resembles those called wolves. It is small, variegated, sharp, and active in jumping. It is called psylla. The other is larger. Its colour is black, and its fore-legs are long. Its movements are slow, and it can scarcely walk. It is not strong, nor capable of jumping. The other kinds, which the dealers in medicine offer for sale, either do not bite at all, or very slightly. 3. There is another kind of those called wolves. One is small, and makes no web, and the larger sort makes a coarse inferior web upon the ground or in hedges. It always makes its web over chinks in the soil, and with the origin of the web in the interior it keeps guard until something falls into the web and moves it, when it comes out. The variegated kind makes a small inferior web among trees.