'/'///; WINGS HOT DERIVED FUO.M TRAdlEAL GILLS 



If we examine the tracheal gills of the smaller dragon-fly (Agrioii >, 

 or the May-flies, or Sialidae, or Perlidae, or PhryganeidaB, we see that 

 they are developed in a very arbitrary way, either at the end of the 

 abdomen, or on the sternum, or from the pleurum ; moreover, in 

 structure they invariably have but a single trachea, from which 

 minute twigs branch out; 1 in the wings there are five or six main 

 tracheae, which give rise to the veins. Thus, in themselves, irre- 

 spective of their position, they are not the homologues of the gills. 

 The latter are only developed 

 in the aquatic representatives 

 of the Neuroptera and Pseudo- 

 neuroptera, and are evidently 

 adaptive, secondary, temporary 

 organs, and are in no sense 

 ancestral, primitive structures 

 from which the wings were 

 developed. There is no good 

 reason to suppose that the 

 aquatic Odonata or Ephemerids 

 or Neuroptera were not descend- 

 ants of terrestrial forms. 



To these results we had 

 arrived by a review of the 

 above-mentioned facts, before 



meeting with 

 opinions, 

 nf flip 

 wiiio-c nf 



Fritz Milller's 



fvnin <stnrlv 

 riom a Stuay 



pnt nf fhp 

 ien 3 



/I^irr 



(v ig. 



FIG. 158. Changes in external form of the 

 young larva of Calotermes ruyosus, showing, in 

 A and , the mode of origin of the wing-pads : .4, 

 newly hatched, with 9 antennal joints, x 8. , older 

 larva, with 10 joints, x 8. C, next stage, with 11 

 joints, x S. D, larva, with twelve joints ; the position 

 of the parts of the alimentary canal are shown : v, 



tViaf " ("\ \ T'Vip crop; m, stomach; f>, "paunch"; e, intestine; r, 

 heart, x ->#. After Fritz Miiller, from Sharp. 



wings of insects have not 



originated from ' tracheal gills.' The wing-shaped continuations of 

 the youngest larvae are in fact the only parts in which air tubes are 

 completely wanting, while tracheae are richly developed in all other 

 parts of the body. 3 (2) The wings of insects have arisen from 



1 Compare the observations of Palmen, Gerstacker, Vayssiere, and others. 



2 Beitrage zur Kenntniss der Termiten. Jenaische Zeitschrift fiir Naturwissen- 

 chaft. Bd. ix, Heft 2, p. 253, 1875. Compare, however, Palme'n's Zur Morphologic des 

 Tracheensystems, Helsingfors, 1877, wherein he opposes Miiller's view and adopts 

 Gegenbaur's. See p. 8, foot-note. 



3 Pancritius, who also adopted Miiller's views, lays much stress on the fact that in 

 larvfe of some orders the tracheae do not enter the rudimentary wings until the end 

 of larval life, and hence the wings have not originated from tracheal gills, but were 

 originally " perhaps only protective covers for the body." 



