EARTH-WORMS AND THEIR WORKS. 291 



the gizzard. The latter organ is lined with a smooth, thick, chitinous 

 membrane, and is surrounded by weak longitudinal but powerful trans- 

 verse muscles. Grains of sand and small stones, from one twentieth 

 to a little more than one tenth of an inch in diameter, may be found 

 in the gizzard and intestines, and are supposed to serve, like mill- 

 stones, to triturate the food. The gizzard opens into the intestine, 

 which presents a peculiar remarkable longitudinal involution of the 

 walls, by which an extensive absorbent surface is gained. The circu- 

 latory system is well developed. Breathing is done by the skin, with- 

 out special respiratory organs. The nervous system is fairly developed, 

 with two almost confluent cerebral ganglia situated near the anterior 

 end. 



Worms have no eyes, and are measurably indifferent to light ; yet 

 they can distinguish night from day, and are quickly affected by a 

 strong light, and after some time by a moderate light shining con- 

 tinuously upon them. They do not much mind a moderate radiant 

 heat, but are sensitive to cold. They have no sense of hearing, but 

 are extremely sensitive to vibrations in any solid object. Worms in 

 pots, which had paid no attention to the sound of a piano, when placed 

 on the piano instantly drew into their holes when the notes were 

 struck. Their whole body is sensitive to contact, as of a puff of air. 

 Their sense of smell is feeble, but responds fairly well to the odor of 

 the cabbage and onion or whatever they like, as was shown to Mr. 

 Darwin by some very interesting experiments. They are omnivorous, 

 and swallow enormous quantities of earth, out of which they extract 

 any digestible matter which it may contain, consume decayed and 

 fresh leaves and vegetable matter, and raw, roasted, and decayed meat, 

 but like raw fat best. 



Mr. Darwin discovered in worms evidences of a degree of intelli- 

 gence. They line their burrows with leaves as a protection, it is sup- 

 posed, against the cold of the clammy ground, and plug the entrances 

 to them with leaves and leaf-stalks. It requires some manipulation to 

 get these leaves in right, but the worms know how to perform it, and 

 can discriminate between the easiest way to draw the leaf in and other 

 ways. Commonly, seventy or eighty per cent of the leaves are drawn 

 in by the tips, that being the direction in which they go in most easily 

 and fold most nicely. Some leaves, however, may be drawn in nearly 

 as easily by the sides or the bases as by the tips, and a larger propor- 

 tion of these are drawn in in those ways. The worm likes to gnaw 

 the base of the petiole of the ash-leaf, and this leaf is drawn in by 

 the base. Pine-leaves, which grow in pairs attached to a single base, 

 must be drawn in by the base or not at all, and the worm rarely makes 

 a mistake in the matter. Mr. Darwin suggests here, however, that we 

 must not suppose the worm to know too much, and that some other 

 quality than mechanical convenience may guide it to the selection of 

 the base of the pine-leaf. Sometimes, when the worm begins to plug 



