536 THE PAXOKPOID COMPLEX, iii., 



Introduction. 

 (Text-fig. 35.; 



The study of the Wing- Venations of the Orders comprising the 

 Panorpoid Complex has proved a difficult and protracted task; 

 and the results, even with the greatest possible amount of con- 

 densation, will occupy quite as much space as can be fairly 

 allotted to a single part of this work. That being so, I have 

 decided to dispense with the usual introductory remarks upon 

 the general scheme of wing-venation, and to embark upon the 

 details of the actual research with the briefest possible indication 

 of the premises on which they are founded. For those who 

 have not yet mastered the Comstock-Needham system, either the 

 earlier work of these authors (14*), or the excellent later book 

 by Comstock (15), will be found to contain all that is necessary 

 for the complete understanding of the venational notation; while 

 Text-fig. 37 reproduces Comstock's original diagram showing this 

 notation applied to his hypothetical venational type. 



As a basis for my study, I have not been content to accept 

 merely the reference to the precedent pupal tracheation, valu- 

 able as it is. It must be recalled that, in three of the Orders 

 with which we have to deal, this pupal tracheation is greatly 

 reduced, and of little value in the determination of homologies. 

 Moreover, since Part 2 was written, two new fossil Orders be- 

 longing to the Complex have come to light (28, 29) ; so that, 

 besides the three recent Orders just mentioned, there are also 

 three fossil Orders, now extinct, to which this method is not 

 applicable . We may put the position thus : — 



(1) Orders only known as fossils: — Protomecoptera, Parame- 

 coptera, Paratrichoptera. 



(2) Recent Orders with reduced pupal tracheation: — Mecop- 

 tera, Trichoptera, Diptera. 



(3) Recent Orders with complete pupal tracheation : — Megalop- 

 tera, Planipennia, Lepidoptera. 



The presence of the complete pupal tracheation is an archaic 

 character; so that the last three Orders named must be regarded 

 as more archaic than the three in (2), for the character men- 

 tioned. It will be at once obvious that no Order in (2) can be 

 ancestral to any one of the Orders in (3) . Those wings, in 

 which the pupal tracheation remains complete, I propose to term 

 holotracJieate; those in which it is reduced, merotracheate. 



"The numbers in brackets refer to the Bibliography at the end of the 

 paper. 



