1930 ] 
Geological History of Insects 
27 
Mecoptera in all deposits! When we put this on a percen- 
tage basis, the results are even more striking (table 2). 
We find that the Mecoptera make up about 9% of the Per- 
mian insect fauna, less than 4% of the Mesozoic, and not 
even .2% of the Tertiary; and as I have mentioned above, 
the Mecoptera contribute less than .04% to the recent spe- 
cies. The Neuroptera comprise about 3% of the Permian 
insects, nearly 5% of the Mesozoic, but less than 1% of the 
Tertiary and Recent. The Odonata are only represented in 
the Permian by less than 1%; but in the Mesozoic we find 
that almost 7 % of the species belong here, while in the Ter- 
tiary the figures drop below 2%, and at the present time the 
Odonata make up about one-half of one per cent. The Ho- 
moptera, as I have stated above, are very common in the 
Permian beds, making up a total of about 12.5 ; in the Meso- 
zoic this changes to 9%, in the Tertiary and Recent to a 
little less than 4%. The Psocoptera are also common in the 
Permian, making up 6% of the fauna; but less than .3% of 
the Mesozoic, .4% of the Tertiary and about .1% of the Re- 
cent. The Coleoptera are rare in the Permian, only about 
1% of the species of this horizon belonging here.; but in the 
Mesozoic, Tertiary and Recent about 40% of the species 
fall within this order. The Plectoptera make about 4% of 
the Permian insects, but this figure drops off gradually 
from the Mesozoic reaching about .1% at present. Approxi- 
mately .3% of the Permian insects are Diptera, and this in- 
creases to 5% in the Mesozoic and 27% in the Tertiary, only 
to drop again in recent times to about 10%. The Orthop- 
tera are as scarce in the Permian as the Diptera but in- 
crease to 9% in the Mesozoic, then fall off to about 2%. 
The Blattaria furnish us with an astonishing decline : in the 
Upper Carboniferous they composed about 57% of the en- 
tire insect world, as we know it ; in the Permian, this figure 
became 34% ; in the Mesozoic, 7% ; and in the Tertiary and 
Recent, less than 1%. 
I have presented these figures without any implications 
as to their significance, or without trying to interpret them. 
It is an undisputable fact that the Mecoptera include 9% of 
the known species of Permian insects, 4% of the Mesozoic, 
and .2% of the Tertiary. We now have to determine 
whether this variation is due merely to chance or to actual 
