THE WINGS OF ODONATA 



225 



based upon irrefutable ontogenetic evidence is largely due to the labors 

 of Professor J. G. Needham. This author, in collaboration with the writer, 

 first traced the development of the venation through a series of nymphal 

 stages (Comstock and Needham 'gS-'gg), and in a later paper (Needham 

 '03) he greatly extended his observations on the venation of the wings of 

 insects of this order. More recently, Tillyard ('14) has made some emen- 

 dations and additions to the nomenclature of parts of the anal area. The 

 following account is based on these three papers. 



While it is easy to recognize the homology of some of the wing-veins of 

 Odonata by a study of wings of adults, there are other veins whose identity 

 was not suspected until the ontogenetic studies referred to above were made. 



The richly veined wing of a dragon-fly, at first sight, shows little in 

 common with the hypothetical type. And even when the tracheation of 

 the wing of an old nymph is studied, there are found some striking dis- 



Fig. 22J.- 



-Wings of nvmphs of Comphus descriptus, early stages 

 (From C. 8z N.) 



crepancies. But in the budding wing of a young nymph we find an 

 arrangement of the trachcce which is almost that of the typical wing. 



Figure 227 represents the tracheation of two nymphs of Gomphus 

 descriptus. The wing figured at A was only one millimeter in length. 

 Here is a costal trachea with some anterior twigs, a subcostal trachea with 

 a terminal fork, a rachal trachea with its sector unbranched, a three- 

 branched medial trachea, a cubital trachea which is two-branched in the 

 usual way, and a single anal trachea with three branches, which may repre- 

 sent the three anal trachea, fused at the base. 



At B in this figure is represented the tracheation of a somewhat older 

 wing, one measuring three millimeters in length. Here the trachea Mi +2 

 has shifted its position and lies across the base of trachea Rg ; and trachea 

 Ml lies in front of trachea Rg. The medial trachea is now four-branched. 

 The costal and anal tracheae are outmn by the others in the occupation of 

 the new territory formed by the growth of the wing, and remain relatively 

 short. 



In the wing of a grown nymph (Fig. .228) is seen the culmination of these 

 tendencies. Trachea M2 has followed trachea Mi ; both of them now lying 



