two
lectures he took four great groups of animals, the Vertebrates, the
Articulata, the Mollusca, and the Radiata, and explained what was the
archetype of each. He shewed the distinctiveness of each plan of
structure, and then discussed the relations of the ideas suggested by
Von Baer to these archetypes. He stated explicitly that while the
adult forms were quite unlike one another, there were traces of a
common plan to be derived from a study of their embryonic development.
Such a trace of a common plan he had himself suggested when he
compared the foundation-membranes of the Medusae with the first
foundation-membranes of vertebrate embryos. This was going a long way
towards modern ideas; but he stopped short, and gave no hint that he
believed in the possibility of the development of one plan from a
lower or simpler plan. The second lecture dealt with the kind of ideas
which were crystallised in the popular but striking work of Chambers,
entitled _Vestiges of Creation_. Chambers attacked the theological
view that all animals and plants had been created at the beginning of
the world, and maintained that geological evidence showed the
occurrence of a progressive development of animal life. Huxley, like
all zooelogists and geologists who knew anything of the occurrence of
fossils in the rocks of past ages, agreed with the general truth of
the conception that a progressive development had occurred which
showed that the species now existing were represented in the oldest
rocks by species now extinct. But the examples he brought forward were
all limited to evolution within the great groups, and did not affect
his idea that archetypes were fixed and did not pass into each other.
Moreover, he summed up strongly against the suggestion that there was
any parallel between the succession of life in the past and the forms
assumed by modern animals in their embryological development. So far
as the present writer is able to judge from study of the literature of
this period, the possibility of evolution was present in an active
form in the minds of Huxley and of his contemporaries, and in an
extraordinary way they brought together evidence which afterwards
became of firstrate importance; but the idea in its modern sense was
rejected by them.

In 1854 Huxley's uncomfortable period of probation came to an end.
Edward Forbes, who held the posts of Palaeontologist to the Geological
Survey, and Lecturer on General Natural History at the M