A little freshwater polyp, about half an inch long, with a crown of tentacles round the mouth. It is seen giving off a bud, a clear illustration of asexual reproduction. When a tentacle touches some small organism the latter is paralysed and drawn into the mouth.] [Illustration: _Photo: J. J. Ward, F.E.S._ EARTHWORM Earthworms began the profitable habit of moving with one end of the body always in front, and from worms to man the great majority of animals have bilateral symmetry.] [Illustration: DIAGRAM ILLUSTRATING THE BEGINNING OF INDIVIDUAL LIFE 1. An immature _sperm_-cell, with 4 chromosomes (nuclear bodies) represented as rods. 2. A mature sperm-cell, with 2 chromosomes. 3. An immature _egg_-cell, with 4 chromosomes represented as curved bodies. 4. A mature egg-cell, with 2 chromosomes. 5. The spermatozoon fertilises the ovum, introducing 2 chromosomes. 6. The fertilised ovum, with 4 chromosomes, 2 of paternal origin and 2 of maternal origin. 7. The chromosomes lie at the equator, and each is split longitudinally. The centrosome introduced by the spermatozoon has divided into two centrosomes, one at each pole of the nucleus. These play an important part in the division or segmentation of the egg. 8. The fertilised egg has divided into two cells. Each cell has 2 paternal and 2 maternal chromosomes.] [Illustration: _Reproduced from the Smithsonian Report, 1917._ GLASS MODEL OF A SEA-ANEMONE A long tubular sea-anemone, with a fine crown of tentacles around the mouth. The suggestion of a flower is very obvious. By means of stinging lassoes on the tentacles minute animals on which it feeds are paralysed and captured for food.] [Illustration: THIS DRAWING SHOWS THE EVOLUTION OF THE BRAIN FROM FISH TO MAN The Cerebrum, the seat of intelligence, increases in proportion to the other parts. In mammals it becomes more and more convoluted. The brain, which lies in one plane in fishes, becomes gradually curved on itself. In birds it is more curved than the drawing shows.] Sec. 6 Great Acquisitions In animals like sea-anemones and jellyfishes the general symmetry of the body is radial; that is to say, there is no right or left, and the body might be halved along many planes. It is a kind of symmetry well suited for sedentary or for drifting life. But worms began the profitable habit of moving with one end of the body always in front, and from worms to man the great majority of animals have bilateral symmetry. They have a right and a left side, and there is only one cut that halves the body. This kind of symmetry is suited for a more strenuous life than radial animals show; it is suited for pursuing food, for avoiding enemies, for chasing mates. And _with the establishment of bilateral symmetry must be associated the establishment of head-brains_, the beginning of which is to be found in some simple worm-types.