lo.l331. 



DRAGON-FLY WING YENATTON-XEEDIIAM. 



713 



:he entrance of the air from a new quarter. And I think that in this 

 jase the necessity may have arisen from the thinninj.- of the ^\mg 

 leases of the slender Zygoptera, whereby the communication of the 

 iradial sector with the radius woukl be gradually pinched oflf. With 

 'the decrease of the air supply from the original source an increased 

 jaraount must needs come from the medial trunk through tracheoles, 

 isome of which would be enlarged and one of which might finally 

 attain the proportions of a tracheal branch, while the base of the 

 radial sector would atrophy." 



Either the attachment of the radial sector to media was made at three 



FIG 7 -TRACHEATION OF THE NODAL REGION OF THE WING. A, OF Didymops transversa say; B, op 

 Cwduleoastrrdiastatops Selys; the latter showing the mode of origin of the two oblique 



VEINS characteristic OF THE CORDULEGASTERIN.'E AND PETALUKIN.I'.. 



different places, or else, since its reattachment, it has taken a different 

 course in each of three difiercnt series within the suborder Zygoptera. 

 In the Lestinix? we find it separating from vein 31, far ])eyond the sub- 

 nodus, the point of its departure marked by a more or less evident 

 ()bli(}uc vein, and a long bridge formed about numerous approxnnated 

 tracheoles, mainly deprived from neigld)oring branches of the media. 

 In the AgrioninjE {s. str.) it separates from vein J/,+. near the nodus, 

 and there is neither bridge nor oblique vein. In Calopteryx it sepa- 



"^ch~^iftin-s of tracheal branches in insects wings are not unprecedented 

 Another instanc-e will be cited further on in the case of the branches of the anal 

 trachea A case of the attaclunent of trachea M, to the radius in Pkr,s has been 

 clearly hKlicated l)y 8puler (Zeitschr. f. Wiss. Zool., Tdll, 1892, lig. 24, and Knder- 

 lein (Zool. Jahrl)., Abt. f. Anat., XVI, 1902, pi. iii, fig. 20.) 



