No. 381.] A HALF-CENTURY OF EVOLUTION. 655 
mentry, France, shows that this was the age of the lower, more 
generalized, or heterometabolous insects, such as cockroaches, 
and other Orthoptera, of Eugereon, may-flies, and possibly 
dragon flies, etc., our wingless stick insects being then repre- 
sented by winged ancestors. At this time also began the 
existence of insects with a complete metamorphosis, as traces 
of true Neuroptera and the elytra of a beetle have been 
detected in Europe. But thus far no relics of flowers or of the 
insects which visit them have been discovered in Carboniferous 
times, not even in the Permian, so that the origin of insects 
with a complete metamorphosis, such as moths, ants, and flies, 
may be attributed to the new order of things, geographical and 
biological, immediately following the Appalachian revolution. 
We do not wish to be understood as implying that the origin 
of new orders and classes is directly due to geological crises or 
cataclysms themselves.! On the contrary, the initial steps seem 
to have been taken as the result of the gradual extension of the 
land masses, and the opening up of new areas; it was the 
period of long preparation, with long-continued oscillations, 
the slowly induced changes resulting from the reduction of the 
mountainous slopes to peneplains, which were most favorable 
to the gradual modification of forms resulting in new types, the 
gradual process of extinction of useless and senile forms, and 
the modification and renewal of those which became adapted 
to the new geographical conditions. 
It should be borne in mind that this extension of the low 
coasts of the continents began in Ordovician times, but the 
remarkable expansion of our continent after the Appalachian 
1T find that Wood has already expressed the same idea more fully, as follows: 
“ Both in the Paleozoic and Secondary periods, therefore, the complete changes in 
the fauna which marked their termination do not appear to have been immediate 
upon the changes of the geographical alignment, but to have required the lapse of 
an epoch for their fulfillment ; and the completeness of that change is perhaps not 
less the indirect result of the altered alignment, by the formation of continents 
where seas had been, and the opening out of new seas for the habitation of marine 
animals, thereby causing a gap in the geological records so far as they have been 
hitherto disc overed, than the direct result of the changed conditions to which the 
inhabitants of the seas, and even those of the land, came to be subject on account 
of the entire change in the alignment of the land over the globe.” (Phil. Mag. 
vol, xxiii, 1862, p. 281.) 
