100 
THE PRINCIPLES OF BIOLOGY. 
stage traits are acquired which successively distinguish the 
developing embryo from groups of embryos that it previously 
resembled, thus step by step diminishing the class of embryos 
which it still resembles ; and thus the class of similar forms 
is finally narrowed to the species of which it is a member.” 
But these resemblances are only general, and not special; 
for example, it would be wrong to say that the human embryo 
at any stage specially resembled a fish, but certainly it passes 
through certain stages during which it possesses more general 
characters which are also possessed by fishes and which it 
loses during its advance towards maturity. Examples of 
passing general resemblances to other classes could be easily 
found, But in many cases there are irregularities, and the 
embryo, instead of advancing to a likeness of a higher type, 
seems to be stationary, or even retrograding. But if we 
assume this development through stages to have some con¬ 
nection with the stages through which the ancestral races of 
the species have passed, we see clearly that it must be so, as 
the modification of organic forms is irregular and does not 
always imply a progress to higher forms. As we found that 
from the relations of languages we derived some good illus¬ 
tration of the facts of classification, it appeared to me 
interesting to try if the facts of embryology could be supported 
by ethnological facts. The development of an embryo is 
evidently analogous to the development of speech in an infant. 
Now it struck me as remarkable that in nearly all European 
languages the first words which an infant learns, those ex¬ 
pressive of the names of the parents, “ Papa,” and “Mamma,” 
are very much alike, even if the words for father and mother 
are different. And besides this we find that when children 
first learn to speak they do not form their sentences gramma¬ 
tically, but put the words together without any inflections. 
We find the same mere combining of words now in some 
Eastern languages, and it may have been the characteristic of 
some common ancestral language. 
The next fact which we have to consider is the substitution 
and suppression of organs. In some cases the embryo, during 
some period of its development, possesses organs which the 
mature form does not possess ; they are either reabsorbed, or 
their function is changed so that they discharge a different 
function in the mature stage. Sometimes they are only partly 
absorbed, and then form, in the mature animal, rudimentary 
organs. As an example, Mr. Spencer quotes the case of the 
development of an allantois in the mammalian embryo. This 
allantois is homologous to the breathing apparatus of birds 
and reptiles during their last embryonic stage. But in the 
