OHIO STATE ACADEMY OF SCIENCE 



do b}' means of their thoracic fins. 



The limitation of the wings to the two paii's of meso — and 

 metathorax must be explained mechanicall}' as more suited for the 

 propulsion of the body in flight. We still see among living insects 

 an luidoubted tendency to the stronger development of one of the 

 pairs of wings. 



Opposed to this view is McMurrich : "Granting a descent of 

 the Pterygota from wingless ancestors, it becomes an interesting 

 problem to discover the origin of the wings. Attemi:)ts have been 

 made to show that the}^ 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, trac]:ieae later pushing 

 out into them and transient indications of outpouchings of the 

 j^rothorax also occur in some eaubryos. It has been suggested that 

 23rimarily 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 suj^port 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 l)ody." 



Aside from the lack of any indication of ]3late-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 apjDcndage of the abdomen and never associated 

 in living forms with any structure or -habit leaning toward tracheal 

 outgrowths to appreciate the difficulties of this suggestion. 



A very full statement of this position was given hv 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 hekl 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 im]3roved condition until 

 they became flexible, i. e., attached bv a rude hinge joint to the 

 tergal plates of the meso- and meta-thorax. Then by continued use 



