282 L. Agassiz on the Primitive Diversity 
daries. And the fragmentary information which we already 
possess upon the insects of Aix in Provence, and those of 
Oeningen, will justify the expectation that insects will finally 
be found very numerous in all the geological periods, from 
that of the carboniferous deposit to the present day; that is 
to say, ever since terrestrial vegetation has had an extensive 
development. The discoveries by Hugh Miller of true trees 
in the old red sandstone, will justify the prophecy that insects 
will be found, some day or other, even among palozoic rocks 
older than the coal period. 
But what of the Vertebrata? Is there not evidence that, at 
the present day, they are more diversified and more numerous 4 
Here again I answer, decidedly, No; granting only that there 
are periods during which the higher classes of these types 
did not exist, and that therefore, as a type the vertebrata of 
the present day are more diversified ; but the individual 
classes, from the time of their appearance, have been in each 
former period as numerous, and even as various, as they are 
at present. 
Let us apply to these the same measure which we have ap- 
plied to the Radiata, Mollusca, and Articulata to justify this as- 
sertion, which seems so completely at variance with our 
knowledge of fossil vertebrata. Fishes occur, as is well 
known, in all geological formations. But should we compare 
the fossil fishes of each geological period, as they are known 
from a few localities, with the whole number of fishes which 
exist all over the world in our day? It would be as unphilo- 
sophical as it would be inconsistent with our knowledge of 
the geographical distribution of animals. Like all other 
living beings, fishes are located within definite boundaries, 
and it will be but fair to compare the fossil species of a given 
locality with the special Ichthyological faunze which occur 
in different oceans, or in different fresh-water basins. Now 
with this rule we may institute a comparison of the fossil 
fishes with the living ones, with reference to their number 
as well as to their variety. 
The number of species of fossil fishes known at present 
from the tertiary deposits, in a single spot upon the Island 
of Sheppy, is greater than the number of fishes which have | 
ee iO a et 
