120 THE LIFE-STORY OF INSECTS [CH. 



and speculate on the origin of wings in the most 

 primitive exopterygote insects, the task becomes still 

 more difficult. Many years ago Gegenbaur (18/8) was 

 struck by the correspondence of insect wings to the 

 tracheal gills of may-fly larvae, which are carried on 

 the abdominal segments somewhat as wings are on the 

 thoracic segments. But Burner has recently (1909) 

 brought forward evidence that these abdominal gills 

 really correspond serially with legs. Moreover Gegen- 

 baur's theory suggests that the ancestral insects were 

 aquatic, whereas the presence of tubes for breathing 

 atmospheric air in well-nigh all members of the class, 

 and the fact that aquatic adaptations, respiratory 

 and otherwise, in insect-larvae are secondary force 

 the student to regard the ancestral insects as ter- 

 restrial. It is indeed highly probable that insects 

 had a common origin with aquatic Crustacea, but all 

 the evidence points to the ancestors of insects having 

 become breathers of atmospheric air before they 

 acquired wings. How the wings arose, what func- 

 tion their precursors performed before they became 

 capable of supporting flight, we can hardly even 

 guess. 



Our study of the life-story of insects, therefore, 

 while it has taught us something of what is going on 

 around us to-day, and has given us hints of the course 

 of a few threads of that long life-story which runs 

 through the ages, brings us face to face with the 



