March, 1916.] CrAMPTON : ORIGIN OF WiNGS. 17 



ready for aerial respiration; and the investigations of Palmen .(1877) 

 have clearly shown that the open respiratory system is the more an- 

 cient, and therefore the original one, while the closed one for aquatic 

 respiration is evidently the product of a process of adaptation to 

 aquatic life which was subsequently acquired. 



Since the open respiratory system for aerial respiration is clearly 

 the more ancient, and hence the original one even in aquatic forms, 

 it is evident that all insects are descended from terrestrial forms, 

 which could not have borne tracheal gills; and we can therefore state 

 with conviction that the wings of modern insects could not have been 

 derived from tracheal gills. The adherents of the tracheal gill 

 theory, however, would attempt to avoid this difificulty by suggesting 

 that although the ancestors of all insects were originally air breathers, 

 the ancestors of the winged forms became temporarily aquatic, and 

 thus acquired the gills which were to develop into wings when they 

 became air breathers once more ! This argument is clearly an at- 

 tempt to again avoid the issue, but is also unavailing! If the ances- 

 tors of winged insects were all gill breathers at one time (which must 

 have been rather recent), why do no fossil forms show traces of 

 such " wing-gills," and why do we have no recent forms which have 

 retained structures suggestive of this common origin of the wings? 

 The Ephemerids cannot be taken as examples of this, since it has been 

 shown (point (i)) that the wings of Ephemerids are not homo- 

 logous with the gills, and the ontogenetic development of no other 

 winged insect offers any hint of such a common origin for the wings 

 in gill-like structures! 



10. Palaeontology shows that the earliest fossil insects had wings, 

 yet these have retained no series of abdominal gills homodynamous 

 W'ith the wings, the only abdominal structures which are homody- 

 namous with the wings being paranota, as has already been pointed 

 out (see point .(S) )• 



11. The great mass of lower pterygote insects are not aquatic, but 

 are terrestrial, whereas if all pterygote insects passed through an 

 aquatic stage, we would expect that the great majority of the lower 

 winged forms would still be aquatic, at least in the immature stages. 

 On the other hand, numerous lower pterygote insects have retained 

 paranota in the prothoracic region, at least, while tracheal gills occu- 

 pying the typical wing location are wanting in all of them. 



