In the hermaphroditic animals the sperm cells of the same individual may fertilize their own egg-cells or ova, as in the feat-worm (self-fertilization), while in the earth worm, although it is also hermaphroditic, cross-fertilization takes place. Two earth-worms mutually fertilize each other, the sperm cells of one fertilize the ova of the other, and the sperm cells of the latter fertilize the ova of the former. _Fertilization in plants._—This mode of cross-fertilization is the one generally found in phanerogamous (φανερός = apparent and γάμος = marriage) plants. In the lower forms of the organic world the line of demarkation between plant and animal is somewhat blotted, and the identity of the mode of fertilization does not need to be particularly emphasized. In the higher forms the division is generally made by the mode of the assimilation of food and of motion. Plants generally break up the inorganic compounds into separate elements and recombine them into organic compounds, or potential energy. These organic compounds serve then the animal as food or as source of energy. The inorganic compounds being, as a rule, ubiquitous, the plants have hence a certainty of food supply and do not depend upon the facility of motion. They are, therefore, marked by a fixity to the soil. They are also surrounded by an outer skeleton, or a coat of cellulose and are less affected by outer stimuli; hence they possess slight consciousness. For the animals the food-supply is more uncertain, hence they need greater movement. For this reason they generally lack the external skeleton and hence possess higher consciousness. Apart from this division plant and animal are closely related cousins, and the mode of fertilization of most of the higher plants is about the same as in the hermaphroditic animals. The sexual organs of the phanerogamous plants are represented by the flowers.[Y] Showy flowers consist usually of four sets of organs, pistils, stamens, petals, and sepals. The sepals taken together constitute the calyx, the petals taken together constitute the corolla. The essential organs of the flower are the stamens and pistils. The stamen represents the male organ, and the pistil the female organ of the plant, while the calyx and corolla form the floral envelopes, or the so-called perianth and are analogous to the external genital organs in the animal. Flowers which contain all the four sets of organs are said to be complete flowers, those which have the essential organs only are called perfect flowers. [Illustration: CUT XXXVI. _A complete flower._ st, stamen; pi, pistil; pe, petal; s, sepal; ca, calyx; c, corolla. After Bergen.]