706 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



responding veins will be designated, beginning at the anterior margini 

 of the wing, by the following names and abbreviations: 



1. Costa [C). -l- Media {M.). 



2. Subcosta{Sc.). •'>• Cuhitns {Cu.). 



3. lindius{R.). 6. Anal veins {A.). 



Typical branches will be designated by added numerals (as J/j, J^,'. 

 J/j, and 3£^, designating from front to rear the branches of the media), 

 except the posterior division of the radius, which has received thei 

 special name of "radial sector" (Es.). Accessory and secondary 

 branches will be designated by small letters added in the order of thei 

 development of the branches (as i?.s',„ i?.s>^, ^.s',.^ etc., for the secondary 

 branches of the radial sector). 



Fig. 1 represents the tracheae in two early stages of the development]' 

 of the nymphal wing of Gomphui^ descrlptus. A is from a nymph less- 

 than one-fourth grown, the wing 1 mm. long. The trachete so closely 

 resemble those in the developing wings of insects of many other orders 

 there can he no doubt as to their homologv. The radial sector is 



Fig. 1. — Trachea.tion of the wings of two nymphs of Oomphus dcscriptus Banks, two early • 



STAGES. For explanation of lettering see text; also, n = nodus and St = SUPERTRIANGLE. I 



simple — it is generally branched in other orders — and there is a single 

 anal vein. In other orders there are oftenest three." Otherw^ise the 

 tracheie are entirely t^^pical at this stage. It is worthy of note that 

 at this stage the wing is somewhat bilaterally symmetrical and the 

 trachea^ are of almost equal size and length. 



Fig 1. B is from an older nymph with wings 3 mm, long. The twc 

 marginal tracheae are reduced or, rather, outstripped by their com- 

 petitors, the wing has become quite unsymmetrical, and the radial 

 sector has come to lie across the distal end of the media. 



Fig. 2 represents the tracheation of both fore and hind wings of a 

 grown nymph of the same species. The costal trachea is so dwarfed 

 as hardly to enter the costal vein. The radial sector lies back of the 

 two anterior branches of the media which it crosses. The othei 

 ti'achea', also, are assuming their definitive positions, and some of them 

 are becoming strongly angulated at the middle and toward the base ol 

 the wing. 



These three stages show clearly how the primitive insect wing ha!-/ 



"Prol)al)ly tlu" three terminal ])rancheHi of this trachea represent the typical tirst. 

 second, and third anal trachetc fused together. 



