290 L, Agassiz on the Primitive Diversity 
ozoa from among Polypi to the class of Mollusks, will en- 
tirely change the aspect and relations of the faune of the 
paleozoic rocks. How different, again, would the order of 
succession of Mollusks appear, were we to adhere to Cuvier’s 
view of separating the Brachiopods, as a class, from the other 
Acephala, to which they are now more correctly referred. 
The vexed question of the period of appearance of Dicotyle- 
donous plants in the geological series would have been set- 
tled long ago, had it been placed upon its real foundation. It 
is not in reality to be argued upon paleontological evidence 
chiefly, for it resolves itself in the main into a botanical ques- 
tion, and the definite answer must depend upon the position 
finally assigned by botanists to the families of Conifere and 
Cycadee. If these natural orders of plants are really allied 
to the Dicotyledone, then this type begins with the paleozoic 
rocks in the Devonian system, and there is no gradation in 
the order of succession of plants during geological times. 
But if the view of Brongniart is more correct, if the Coniferz 
and Cycadez have to be separated from the Dicotyledone as 
Gymnosperme, and if, moreover, these latter should prove, as 
I believe they are, inferior even to the Monocotyledonee, then 
we may at once recognise in the vegetable kingdom a similar 
gradation of types as among animals. These examples may 
suffice to show what is required for a proper investigation of 
the order of succession of organized beings in the course of 
time, and how little confidence the investigations in this field 
deserve, which have not been made with due reference to all 
the points mentioned above. It is indeed only in the classes, 
the structure and embryology of which is equally well under- 
stood, weare able to discover thelaws regulating the succession 
of animals and plants in geological formations, and our know- 
ledge is at present still too imperfect to carry the investiga- 
tion into all families of the animal kingdom. And yet enough 
is known to leave no doubt as to the final result; we may con- 
fidently await the time when the glory of the wonderful order 
of creation shall be fully revealed to us, and this may stimu- 
late us to renewed efforts, since the success depends entirely 
upon our own exertions. 
The geographical distribution of animals began only to be 
