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 tlieir ancestry. More- 

 over, the most ancient fossil foxms 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 su.ch 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- 

 dently from extreme specialization in recent time. 



It seems very diflficult, however, to conceive of any condition 

 outside of water which cO'uld furnish the basis for development 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 suflicientl}^ develoiDed 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 gills 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 winged form Ave 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 Avith many resulting 



