24 
Psyche 
[March 
developed along the lines of the recent species that it seems 
almost certain that the order must have existed in the Per- 
mian. The Trichoptera of the Jurassic, on the other hand, 
are essentially more primitive than the extant species, many 
of them possessing a venation so similar to that of their 
contemporary Mecoptera that it is frequently difficult to 
distinguish the members of these two orders. Consequently, 
it is very doubtful if the caddis-flies will ever be found lower 
than the Triassic. The Hymenoptera are first represented in 
the Jurassic, by such forms as Siricoids, Oryssoids, and 
Ichneumonoids. This diversity of the Jurassic Hymenop- 
tera makes it rather obvious that the order had been some 
time in existence before that period, probably at least as far 
back at the lower Triassic. The only known Mesozoic Der- 
maptera and Thysanoptera have been taken in the Turk- 
estan beds, but they are both represented by characteristic 
types, not very much unlike certain recent species. 
We are now left with the two orders whose first record is 
in the Tertiary rocks, — the Lepidoptera and Isoptera. Only 
very few Lepidoptera have been found as fossils in this 
horizon, but these are absolutely modern in every respect, 
and there can be no doubt that the group arose some time in 
the Mesozoic. The Isoptera are quite common in the Ter- 
tiary beds and are differentiated into many recent families, 
most of which, however, are now limited to much smaller 
geographical areas. There is every indication that the ter- 
mites will some day turn up in Jurassic and perhaps even 
Triassic strata. 
From the foregoing discussion of the geological ranges 
of the larger insect orders, it is obvious that by far most 
of the orders have had a longer history than one would as- 
sume from the mere geological occurrence of the oldest 
species. In every case where we have enough fossils to util- 
ize, we see that the earliest representatives of each order 
are relatively highly specialized along the lines of the re- 
cent types ; and this is particularly true of the Permian rec- 
ord. In order to have our diagram represent the probable 
true range of these orders, we must make several changes : 
The Mecoptera, Neuroptera, Odonata, Homoptera, Psocop- 
tera, Plectoptera, and of course the Blattids, would extend 
back to the Upper Carboniferous ; the Hemiptera would re- 
cede to the Permian, and the Trichoptera, Dermaptera, and 
