te 
: 
98 Professor Agassiz on the Distribution of Fossils. 
that the male and female of a species have been made types of 
different genera ; a circumstance which has also occurred in 
regard to differences of age. These, therefore, cannot be re- 
cognised by resemblances, but by their whole relations. I do 
not doubt that, at a future time, ¢é will become necessary to 
express the specific difference of organic remains by the circum- 
stances of their occurrence, without tt being possible to assign 
distinctions to them. Instead, then, of being involved in 
boundless uncertainty, our science will emerge from its dry 
foundation to a state of rich development. 
In reference to the above letter, Professor Bronn of Heidel- 
berg remarks : “It is hardly necessary to say, that my views 
do not agree with those expressed by Professor Agassiz on 
Trigonie; for the latter are in opposition to the principles 
followed in my Lethiia Geognostica, although I am far from 
wishing to assert that the forms which I have in other places 
united under any one species, according to the materials I 
possessed at the time, have been in all cases confirmed as va- 
rieties of one species, by the assistance of richer materials and 
direct autopsy. I am, however, convinced, that there are 
species which pass from one subdivision of a formation into 
another, and even from one formation into another; and, in- 
stead of fettering myself by the preliminary assertion that no 
species occurs in two formations (as Agassiz does in the Mem, 
de Neuchat. ii. 17); or, instead of assuming that there are 
species which cannot be distinguished by any extérnal charac- 
ters, but only by their exterior relations (that is, in the case 
before us, little else but their geognostical and geological rela- 
tions), I unite under one species all forms which can be proved 
to derive their origin from one and the same kind of ancestors 
(as in zoology and botany generally), or which do not differ 
from these more than they do among themselves; and I am of 
opinion that, at the same time, many distinctions adhering to 
individuals are merely the result of the influence of the rela- 
tions of the external world.”* 
* From the Neues Jahrbuch fiiv Mineralogie, Geognosie, &e- 
