creatures which Huxley selected and placed
together, with the addition of the sea-anemones and the medusa-like
Ctenophora, which, indeed, he mentioned in his memoir as being related
to the others, but reserved fuller consideration for a future
occasion. This group is now called the Coelenterata, the name
implying that the creatures are simply hollow stomachs, and it is
contrasted in the strongest way with the group Coelomata, in which
are placed all the higher animals, from the simplest worm up to man;
animals in which, in addition to the two foundation-membranes of the
Coelenterata, there is a third foundation-membrane, and in which, in
addition to the simple stomach cavity with its offshoots, there is a
true body-cavity or coelome, and usually a set of spaces and
channels containing a blood-fluid. The older method of naming groups
of animals after some obvious superficial character lingered on for
some years in text-books and treatises, but in this memoir the young
ship-surgeon had replaced it by the modern scientific method of
grouping animals together only because of real identity of structure.

There is yet left to be noticed perhaps the most wonderful of all the
ideas in this first memoir by Huxley. In the course of describing the
two foundation membranes of the Medusae he remarks:

"It is curious to remark, that throughout, the outer and inner
membranes appear to bear the same physiological relation to one
another as do the serous and mucous layers of the germ: the outer
becoming developed into the muscular system, and giving rise to
the organs of offence and defence: the inner on the other hand
appearing to be more closely subservient to the purposes of
nutrition and generation."

In the whole range of science it would be difficult to select an
utterance more prophetic of future knowledge than these few words.
Huxley had been reading the investigations of Von Baer into the early
development of back-boned animals. He had learned from them the great
generalisation, that the younger stages of these animals resemble one
another more closely than the adult stages, and that in an early stage
in the development of all these animals the beginning of the embryo
consists of two layers of cells, in fact of two foundation-membranes,
one forming specially the wall of the future digestive canal, the
other forming the most external portion of the future animal. In these
days nothing could