336 OHIO STATE ACADEMY OF SCIENCE 
do by means of their thoracic fins. 
The limitation of the wings to the two pairs of meso — and 
metathorax must be explained mechanically as more suited for the 
propulsion of the body in flight. We still see among living insects 
an undoubted tendency to. the stronger dey elopment. of one of the 
pairs of wings. 
Opposed to this view is MeMurrich: “Granting a descent of 
the Pterygota from wingless ancestors, it becomes an interesting 
problem to discover the origin of the wings. Attempts have been 
made to show that they are modified tracheal branchiae, a theory 
which necessitates the derivation of the Pterygota from aquatic 
ancestors. Such a derivation, however, is unsupported by any 
evidence at present at our disposal, it being much more probable 
that the immediate ancestors of the Pterygota were terrestrial, just 
as Campodea is today. The wings arise in the embryo as dorsal 
outpouchings of the meso- and meta-thorax, tracheae later pushing 
out into them and transient indications of outpouchings of the 
prothorax also occur in some embryos. It has been suggested that 
primarily the wings were plate-like outgrowths on the thoracic 
segments which served to break the fall and increased the distance 
traversed by jumping insects, and in support of this view the fact 
may be mentioned that many Apterygota are saltatorial. The 
limitation of the wings to the meso- and meta-thorax may stand in 
some relation to the center of gravity of the body.” 
Aside from the lack of any indication of plate-like growths 
for respiration as here necessitated, it is only necessary to mention 
the fact so well known to all students of insect structure that the 
saltatorial Apterygota are a much specialized group, the saltatorial 
organ a bent-under appendage of the abdomen and never associated 
in living forms with any structure or habit leaning toward tracheat 
outerowt hs to appreciate the difficulties of this suggestion. 
A very full statement of this position was given by Dr. Pack- 
ard in 1883 and since this was repeated quite fully in his recent 
text-book in 1898 it may be considered as the position held until his 
death. 
“Now, speculating on the primary origin of the wings, we 
need not suppose that they originated in any aquatic form, but in 
some ancestral-land insect related to existing cockroaches and 
Termes. We may imagine that the tergites (or notum) of the 
two hinder segments of the thorax grew out laterally in some leap- 
ing and running insect; that the expansion became of use in aiding 
to support the “body in its longer leaps, somewhat as the lateral 
expansions of the body aid the flying squirrel or certain lizards in 
supporting the body during their leaps. By natural selection these 
structures would be transmitted in an improved condition until 
they became flexible, i. e., attached by a rude hinge joint to the 
tergal plates of the meso- and meta-thorax. Then by continued use 
