=Reproduction.=--When one individual animal produces both sperm cells and egg cells, it is said to be hermaphrodite. This is true of the earthworm. The egg cell is always fertilized, however, not by the sperm cells of the same worm, but by sperm cells formed by another worm. The openings of these ova or _egg glands_ consist of two pairs of small pores found on the ventral surface of the fourteenth and fifteenth segments in most species (see Fig. 77). There are also two pairs of small _receptacles_ for temporarily holding the _foreign sperm cells_. One pair of the openings from these receptacles is found (with difficulty) in the wrinkle behind the ninth segment (Fig. 77), and the other pair behind the tenth segment. The _sperm glands_ are in front of the ovaries (Fig. 77), but the _sperm ducts_ are longer than the _oviducts_, and open behind them (Figs. 77, 78). The worms exchange sperm cells, but not egg cells. The reproductive girdle, or _clitellum_, already spoken of, forms the case which is to hold the eggs (see Fig. 71). When the sperm cells have been exchanged, and the ova are ready for fertilization, the worm draws itself backward from the collarlike case or clitellum so that it slips over the head. As it passes the fifteenth and sixteenth segments, it collects the ova, and as it passes the ninth and tenth segments, it collects the sperm cells previously received by touching another worm. The elastic, collar-like clitellum closes at the ends after it has slipped over the worm’s head, forming a _capsule_. The ova are _fertilized in this capsule_, and some of them hatch into worms in a few days. These devour the eggs which do not hatch. The eggs develop into complete but very small worms before the worms escape from the capsule. [Illustration: FIG. 78.--Side view showing setæ, nephridia pores, and reproductive openings.] =Habits.=--The earthworm is omnivorous. It will eat bits of meat as well as leaves and other vegetation. It has also the advantage, when digging its hole, of _eating the earth_ which must be excavated. Every one has noticed the fresh “casts” piled up at the holes in the morning. As the holes are partly filled by rains, the casts are most abundant after rains. The chief _enemies_ of the earthworm are moles and birds. The worms _work at night_ and retire so early in the morning that it takes a very early bird to catch a worm. Perhaps the nearest to an intelligent act the earthworm accomplishes is to _conceal the mouth of its hole_ by plugging it with a pebble or bit of leaf. They _hibernate_, going below danger of frost in winter. In dry weather they burrow several feet deep.