24 CLAUDE I'ULLEE.' 



Further, in mature nymphs the median trachea is in contact 

 with either the radial or the cubital in the base of the wing- 

 sac ; in the figures it is shown separated. 



II. THE ORIGIN OF WING- VENATION. 



The wings of termites seem to be the final form of pouch- 

 like expansions of the meso- and metathorax. Trachea? are 

 not absent from " the wing fundaments '' as has been stated, 

 and the buds, from which later on they develop, certainly 

 form before any thoracic extension is noticeable. 



In 1906 Woodworth^ developed a general theory of wing- 

 venation which suffered criticism because he ignored, or set 

 out to controvert, the accumulated evidence shoAving the 

 venation of the insect-wing to be derived from the tracheation 

 of the developing organ, or, as he rather sceptically puts it : 

 " The veins simply represent the tracheal arrangement." He 

 ai'gued : " The more rational conception is that there existed 

 at the beginning and has existed through all time to the 

 present day, a mechanical necessity, in accordance with which 

 the primitive venation was ])roduced and all its essential 

 features have been maintained through all the vicissitudes of 

 the ages . . . mechanical necessities are the dominant 

 factor in their (the veins) first production and in their subse- 

 quent development." This theory nuiy be said to apply to 

 the ontogeny of wing-ribs described by Lowne,- as follows : 

 " The walls of the wing-sac become plicated in fan-like folds, 

 radiating from its attachment to the thorax, the angles of 

 the folds become thickened and form the primary veins." 



Whilst the elaboration of AVoodworth's theory finds no 

 place here, his suggestion of a marginal vein is important. 

 He says little more than this : " One of the first veins to 

 appear is the margiiuil. . . . The nuirginul vein is often 

 not uniform in size around the whole wing, being usually 

 strongest on the front nuirgin, often weak on the hind margin, 



' Woodwortli. C. W.. •" The Wing Veins of Insects." " University of 

 (';ilifornia. Teclmiciil Bnlletiiiss.' vol. i. pt. i. lIXMi. 

 - Jjinvne, B. T., " Tlie Blow Fly," Loudon. llsUU-j. 



