338 OHIO STATE ACADEMY OF SCIENCE 
validate this view, was in the absence of any primitive aquatic 
form, all aquatic groups showing most positive evidence of being so 
_by secondary adaptation. The great majority of insects and prac- 
‘tically all members of some orders have no aquatic stages nor do 
they show any trace of aquatic elements in their ancestry. More- 
over, the most ancient fossil forms known have been distinctly 
terrestrial in character, nor do we have any trace of appearance 
of forms that can be referred to modern groups aquatic in char- 
acter until considerably later in the geological record. 
The generalized and very ancient orthoptera, for example, have 
nowhere aquatic stages or indication of any such habit. All the 
aquatic insects of the present time, moreover, have best of evidences 
of being primarily terrestrial, their aquatic habit an adaptation and 
in most cases the evidence of adaptation indicating fairly recent 
resort to that habit. Practically all aquatic forms ‘retain tracheal 
respiration showing indisputable evidence of adaptation from aerial 
life, the few cases of blood gills — as in Simulidae — resulting evi- 
dencly from extreme specialization in recent time. 
It seems very difficult, however, to conceive of any condition 
outside of water which could furnish the basis for dev elopment of 
a tracheated membranous expansion from the body wall, the origin 
of such organs direct for the purposes of flight being excluded from 
consideration on the ground that no such organ could be of any 
functional service till sufficiently developed to serve some purpose 
in locomotion. Further the manner of articulation of wings to 
body, the fact that their movement is secured by movements of the 
body wall, not by direct muscular action, is excellent proof that 
they were first. developed for some other function than flight. 
Moreover, such structures are paralleled by the tracheal aills of 
some modern aquatic forms. 
We are forced then to the ground that the development of the 
tracheal membrane was in water, and we are shut out from con- 
sidering any of the existing aquatic groups as furnishing a basis 
as the ancestral aquatic form. 
We are left then with one other alternative and this on careful 
examination seems to offer a really satisfactory solution for the 
problem. That is, that back of the earliest fossil winged insect 
such as Protocimex, Paleoblattina, or the first of the Paleoblattidae 
there must have been an aquatic form which in its adaptation to 
aquatic life developed tracheal gills in the form of membranous 
tracheal expansions on the two hinder thoracic segments; that this 
hypothetical form changed its habitat to land and the membranous 
structures instead of being lost were modified into wings. Then 
from this primitive w inged form we have by divergence the various 
groups of orders of modern insects established and in some of 
these by adaptation again to aquatic existence we have in many 
instances a well developed aquatic stage with many resulting 
