340 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1953 



stages. The first of these stages was a wingless insect, exemplified in 

 our existing fauna by two orders, the Thysanura (silverfish) and the 

 Entotrophi. The existence of such a phylogenetic group of wingless 

 insects, termed the Apterygota, is based on the premise that wings 

 evolved after the origin of insects and not with their origin — a concep- 

 tion that has been almost universally accepted by zoologists for fully 

 60 years. The opposite view, based on the belief that the first true 

 insects were winged and that all wingless species are secondarily so, 

 was advocated by Handlirsch [2, 3] ; it was a corollary to his convic- 

 tion that insects arose directly from trilobites, the lateral lobes of 

 which became functional wings. So far as I am aware no one who 

 has given serious thought to the subject, with the exception of Hand- 

 lirsch, has accepted this idea. It is true that the wingless Apterygota 

 are known only as far back as the Triassic period and that the winged 

 insects, or Pterygota, extend to the Upper Carboniferous. However, 

 apart from a few Baltic amber inclusions, only two specimens of 

 Apterygota have been found in all geological strata. Their fragility 

 and the very absence of wings, of which most fossil insects consist, 

 make their chances of preservation as fossils very slight indeed. This 

 is an instance in which the structure of living material furnishes more 

 evidence than the geological record. 



DEVELOPMENT OF WINGS 



The second stage in the evolution of the insects began with the de- 

 velopment of wings. The time when these appendages started to 

 appear is not established, but three specimens of insects with fully 

 developed wings have been found in the lowest of the Upper Carbon- 

 iferous strata. Since these specimens belong to different orders, we 

 can only conclude that wings began to evolve in the Lower Carbon- 

 iferous period. However, even if the Upper Carboniferous record 

 is accepted as the time of wing development, it is clear that the insects 

 attained flight fully 50 million years before the reptiles and birds 

 did — a period of time during which the insects, so far as is known, 

 were the sole inhabitants of the air as aerial creatures. By the time 

 flying reptiles and birds had evolved, the insects were well established 

 in their new environment. It is intriguing, though futile, to reflect 

 on the possibility that if the insects had not taken to the air before 

 the vertebrates, they might never have successfully attained flight. 

 The significance of flight for insects was undoubtedly great during 

 the late Paleozoic. This was the age of amphibians and small rep- 

 tiles. Scorpions, spiders, and spiderlike arachnids, belonging to ex- 

 tinct orders, were abundant. All these predators unquestionably 

 subsisted to some extent, and probably to a great extent, on the wing- 



