26 THE TRACHEATION OF WINGS 



trachea are within the thorax of the adult insect, and are thus beyond the 

 influence of the migrations of the wing- veins. 



"It is probable that these changes have to do with improving the air 

 supply of the wing; but we have not sufficient data, as yet, to warrant a 

 definite statement on this point. The important thing for the purpose of 

 the present discussion is that one must know of this tendency on the part 

 of the medial trachea to migrate along the transverse basal trachea in order 

 to be able to recognize it in its various positions." 



In taking up the subject again, in the course of the preparation of the 

 present essay, it occurred to me that there are certain modifications of the 

 wing venation in certain insects that may be due to the same cause as that 

 which causes the migration of the base of the medial trachea along the 

 transverse basal trachea. For example, if the large trachea that supplies 

 the cubito-anal group of tracheae with air affords a better supply of air to 

 the wing than does the trachea that supplies the costo-radial group of 

 trachese, this may be the factor that determines in the wings of dragon-flies 

 the invasion of the area of the radial sector by some of the branches of 

 the media. 



It seemed worth while, therefore, to make a special study of the basal 

 connections of the two large trachese that supply the wing with air. This 

 investigation was undertaken, at my suggestion, by Mr. R. N. Chapman; 

 and the work was done in the entomological laboratory of Cornell Univer- 

 sity, where I had the pleasure of following it step by step. 



The investigation was a very difficult one, involving the making of a 

 large number of most delicate dissections; but it was prosecuted in a most 

 successful manner. We now know the facts regarding the basal connec- 

 tions of the trachea of the wings in most of the orders of insects. 



The results of this investigation have not shown that the air supply of 

 the cubito-anal group of trachese is better than that of the costo-radial 

 group. It does not seem probable, therefore, that an improvement of the 

 air supply to the wing is the factor that has determined the migration of 

 the base of the medial trachea, when it occurs, or the invasion of the area of 

 the radial sector by branches of media in the Odonata and Ephemerida. 



In order that the data now at hand bearing on this problem may be kept 

 together, I publish Mr. Chapman's account of the results of his investiga- 

 tion as an appendix to this chapter. 



