ll up the gap. In its development every animal to-day begins
as an egg. This is a simple cell, and the animal goes through a series
of changes which eventually lead to the adult. Now these changes appear
for the most part to be parallel to the changes through which the
earlier forms of life passed in their development from the simple to the
more complicated forms. Where it is possible to follow the history of
the groups of animals from their fossil remains and compare it with the
history of the individual animal as it progresses from the egg to the
adult, there is found a very decided parallelism. This parallelism
between embryology and past history has been of great service in
helping us toward the history of the past. At one time it was believed
that it was the key which would unlock all doors, and for a decade
biologists eagerly pursued embryology with the expectation that it would
solve all problems in connection with the history of animals. The result
has been somewhat disappointing. Embryology has, it is true, been of the
utmost service in showing relationships of forms to each other, and in
thus revealing past history. But while this record is a valuable one, it
is a record which has unfortunately been subject to such modifying
conditions that in many cases its original meaning has been entirely
obliterated and it has become worthless as a historical record. These
imperfections in regard to the record were early seen after the
attention of biologists was seriously turned to the study of embryology,
but it was expected that it would be possible to correct them and
discover the true meaning underlying the more apparent one. Indeed, in
many cases this has been found possible. But many of the modifications
are so profound as to render it impossible to untangle them and discover
the true meaning. As a result the biologist to-day is showing less
confidence in embryology, and is turning his attention in different
directions as more promising of results in the line desired.

But although the teachings of embryology have failed to realize the
great hopes that were placed upon them, their assistance in the
formulation of this history of the machine has been of extreme value.
Many a bit of obscurity has been cleared up when the embryology of
puzzling animals has been studied. Many a relationship has been made
clear, and this is simply another way of saying that a portion of this
history of life has been read. This aid of emb