26 THE INTERNATIONAL MONTHLY. 
these extinct members at once reveals the fact that the detailed 
skeletal resemblances were not found in the common ancestor, 
but have been separately acquired in the two lines. 
Comparative anatomy deals only with the assemblage of ani- 
mals now existing, a very small fragment compared with the vast 
host of living things that have altogether vanished from the earth. 
In this lies the difficulty of reaching firmly fixed conclusions as 
to animal relationships by the comparative method alone. It 
is like attempting to work out the derivations of the words in a 
language which has no written literature to register its changes. 
Obviously, the etymology of such a language would be well-nigh 
impossible. 
The second method of attacking the genealogical problem is 
embryology. No department of science received a greater im- 
pulse and stimulus from the theory of evolution than this, for 
it was long regarded as the final arbiter in questions of homology 
and relationship. It was believed that the development of the 
individual from the egg (ontogeny) repeated the history of the 
species (phylogeny). This was the u recapitulation theory," or 
the "fundamental biogenetic law" of Haeckel, and according to 
it, embryology rendered other methods of investigation all but 
superfluous. As is the case with most fashions, scientific or 
otherwise, this theory was pushed a great deal too far, and has 
lately fallen into discredit. It was early seen that nearly allied 
animals had often quite different modes of development, and that 
embryological results were frequently in direct contradiction with 
each other, and the climax was reached by the discovery of 
Brooks and Herrick that one and the same species of the crusta- 
cean genus Alpheus displayed several quite different methods of 
development. The adults of this species are alike, and yet, in 
three different localities, three different modes of development 
have been observed, two of them quite radically unlike. It has 
been attempted to break the force of these facts by assuming that 
the embryological record had been obscured, and to some extent 
falsified by the omission of stages and by the introduction of new 
features, which had been imposed upon, or substituted for, those 
