418 Miscellaneous. 
tertiary mammalia of South America and of Australia; and this, I 
have no doubt, will be found to be also the case for the older forma- 
tions, within certain limits, not yet ascertained. The specific differ- 
ences between the remains of the same age, found in deposits remote 
from each other, are daily brought out more distinctly ; and since I 
have begun to compare the fossils of America with those of Europe, 
T am gradually led to infer that no specific identity is likely to be 
established, finally, between animals which have lived at great di- 
stances from one another, even though they were contemporaries. 
The doctrine of the identity of fossils of the same age will therefore 
require great modifications. I am already certain that species of the 
same family, belonging to different epochs, but found in corresponding 
zones of latitude, are frequently much more closely allied than species 
of the same age belonging to different zones. The time is therefore 
fast approaching when zoological affinity alone will no longer be a 
trustworthy criterion of contemporaneity, nor zoological difference, 
however striking, be taken as evidence of a difference in geological 
age. ‘This unexpected and probably to many most unwelcome result 
I have obtained by a careful comparison of many faunee of past ages, 
arranged in the manner above indicated. If this should render the 
identification of rocks, by the aid of the fossils they contain, more 
difficult for those not very familiar with zoology, it will, on the other 
hand, afford most instructive evidences of the successive changes the 
animal creation has undergone upon different parts of the earth’s sur- 
face, at different periods, and show how, in earlier ages, combinations 
of living beings existed in certain parts of the globe, quite distinct 
from those now occupying the same localities, and yet quite similar 
to those existing at the present time in other regions. I need only 
allude to the similarity of some of the extinct faunse of the jurassic 
period to the living fauna of Australia, to make this statement clear ; 
and similar resemblances may be traced between the extinct faunee 
of other periods and the living faunz of other parts of the world. 
As one instance already pointed out, on another occasion, I may 
allude to the resemblance of the extinct fauna and flora of Oeningen 
with that of the temperate zone of the Atlantic States of North 
America. 
A third kind of collections embraces everything that may illustrate 
the mode of reproduction, and the embryonic growth of each class. 
Here are placed together eggs and embryos in various stages of de- 
velopment, and young animals which have not yet completed their 
growth and assumed their specific characteristics. But these col- 
lections do not include the preparations intended to illustrate the 
organs of reproduction themselves, as characteristic of the different 
families in the adult state ; these are referred to the general systema- 
tic collection. 
An objection may perhaps be made to such an arrangement of a 
museum, as requiring a larger number of specimens than are generally 
exhibited in a systematic collection, embracing in one series the whole 
animal kingdom. It would certainly be a great mistake to neglect 
these multiplied modes of instruction, even were it true that they en- 
