aks up in
liberating the germ-cells, but the head-end remains fixed in a crevice
of the coral, and buds out a new body at leisure.

Along with the evolution of the ways of avoiding death should be
considered also the gradual establishment of the length of life best
suited to the welfare of the species, and the punctuation of the
life-history to suit various conditions.

[Illustration: _Photo: J. J. Ward, F.E.S._

GREEN HYDRA

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 draw