THE EVIDENCE FROM THE LIFE-HISTORIES OF INSECTS. 267 



breathing function, and not that of flying, was the first use to which 



the earliest insect wings were put. 



The first beginnings of wings probably existed as we see the 



thin skin-folds of the water-living young (Fig. 179) of some insects 

 to exist to-day that is, as primitive organs 

 adapted for breathing air from water (Fig. 179). 

 One singular little water larva, that of Chloeon 

 (Fig. 171), one of the Ephemeridce or "day-flies," 

 possesses side expansions for breathing, which are 

 moved by muscles, as are the wings; and from 

 what is known of other insect larvae inhabiting 

 water, it seems highly probable that a pair of these 

 flat "gills" to each joint of the body (Fig. 179) 

 may have originally been developed. The next 

 stage in the evolution of the wing from this side 

 gill within which, be it noted, the breathing tubes 

 branch out would consist in these " gills " being 

 employed as agents of aquatic flight that is, flight 

 under the water. In time, the hinder gills would 

 alone be devoted to breathing, whilst those of the 

 middle of the body, being the most advantageously 

 placed for locomotion, would become the wings. 

 Probably the first insect wings were used to propel 

 their possessors under water. Such a state of 

 FIG. 180. POLVNEMA. matters is now seen in Polynema natans (Fig. 180), 

 a, antenna; which Sir John Lubbock discovered in 1862. 



c, rudiments of wines : n->i /-, , j ij 



d, rudiments o fie|s. i hereafter, to movements under water would 

 succeed movements on the surface, and as the 

 muscular developments progressed, the beginnings of aerial flight 

 would be simply a matter of time. The late acquirement of wings 

 in the developing insect of to-day, is thus a fact not without its 

 due significance. Such an event clearly enough shows us, firstly, 

 that flight was a power superadded to insect locomotion long after 

 the evolution of the race from some primitive wingless type ; and 

 secondly, that wing-power was" evolved through the intermediate 

 stage of gills still represented in the water-living larvae (Fig. 179) 

 of our day-flies and their near kith and kin. 



As Gegenbaur remarks, the wings correspond in nature with the 

 gill-processes just described, "for they do not only agree with them 

 in origin, but also in their connection with the body and structure." 

 " It is quite clear," the same authority continues, " that we must 

 suppose that the wings did not arise as such, but were developed 

 from organs which had another function, such as the tracheal gills ; 

 I mean to say that such a supposition is necessary, for we cannot 

 imagine that the wings functioned (or acted) as such in the lower 



