404 
DARWINISM 
CHAP. 
in the Oolite; while ants, representing the highly specialised 
Hymenoptera, have occurred in the Purbeck and Lias. 
This remarkable identity of the families of very ancient 
with those of existing insects is quite comparable with the 
apparently sudden appearance of existing genera of trees in 
the Cretaceous epoch. In both cases we feel certain that we 
must go very much farther back in order to find the ancestral 
forms from which they were developed, and that at any 
moment some fresh discovery may revolutionise our ideas as 
to the antiquity of certain groujos. Such a discovery was 
made while Mr. Scudder’s work was passing through the press. 
Up to that date all the existing orders of true insects appeared 
to have originated in the Trias, the alleged moth and beetle of 
the Coal formation having been incorrectly determined. But 
now, undoubted remains of beetles have been found in the Coal 
measures of Silesia, thus supporting the interpretation of the 
borings in carboniferous trees as having been made by insects 
of this order, and carrying back this highly specialised form of 
insect life well into Palaeozoic times. Such a discovery renders 
all speculation as to the origin of true insects premature, 
because we may feel sure that all the other orders of insects,, 
except perhaps hymenoptera and lepidoptera, were contempo¬ 
raneous with the highly specialised beetles. 
The less highly organised terrestrial arthropoda—the 
Arachnida and Myriapoda—are, as might be expected, much 
more ancient. A fossil spider has been found in the Carboni¬ 
ferous, and scorpions in the Upper Silurian rocks of Scotland, 
Sweden, and the United States. Myriapoda have been found 
abundantly in the Carboniferous and Devonian formations ; 
but all are of extinct orders, exhibiting a more generalised 
structure than living forms. 
Much more extraordinary, however, is the presence in the 
Pakeozoic formations of ancestral forms of true insects, termed 
by Mr. Scudder Paknodictyoptera. They consist of general¬ 
ised cockroaches and walking-stick insects (Orthopteroidea); 
ancient mayflies and allied forms, of which there are six 
families and more than thirty genera (Neuropteroidea); three 
genera of Hemipteroidea resembling various Homoptera and 
Hemiptera, mostly from the Carboniferous formation, a few 
from the Devonian, and one ancestral cockroach (Pakeoblattina) 
