place; and the fertilized egg develops into a new organism. But the
other cells, which have been all the time nourishing these, seem now
to lack nutriment, strength, or vitality to give rise to a new
colony. They die.

We find thus in volvox division of labor and corresponding
difference of structure or differentiation; certain cells retain the
power of fusing with other corresponding cells, and thus of
rejuvenescence and of giving rise to a new organism. And these
cells, forming a series through all generations, are evidently
immortal like the protozoa. Natural death cannot touch them. These
are the reproductive cells. The other cells nourish and transport
them and carry on the work of excretion and respiration. These
latter correspond practically to our whole body. We call them
somatic cells. In volvox they are entirely subservient to, and exist
for, the reproductive cells, and die when they have completed their
service of these. The body is here only a vehicle for ova.
Furthermore, in volvox there has arisen such an interdependence of
cells that we can no longer speak of it as a colony. The colony has
become an individual by division of labor and the resulting
differentiation in structure.

But hydra gives us but a poor idea of the coelenterata, to which
kingdom it belongs. The higher coelenterata have nearly or quite
all the tissues of higher animals--muscular, connective, glandular,
etc. And by tissues we mean groups of cells modified in form and
structure for the performance of a special work or function. The
protozoa developed the cell for all time to come, the coelenterata
developed the tissues which still compose our bodies. But they had
them mainly in a diffuse form. A sort of digestive and reproductive