BY R. J. TILLY ARD. 651 



Hence we conclude tliat tlie Archetype of this interestinij 

 Order must have possessed at least some portions of the aphanto- 

 neuric arcliedictyon; that it also possessed inicrotrichia of small 

 size; and that the maci'otrichia, though remaining as slender, 

 flexible hairs upon the veins, were largely interspersed with true 

 scales upon the wing-membrane, such scales being of elongate, 

 lanceolate form, with few stride. 



We have now to review the above evidence, in order to dis- 

 cover what light it throws upon the Ph^^logeny of the Orders 

 included in the Panorpoid Complex. 



First of all, it must be evident that, as far as the Wing-tri- 

 chiation is concerned, all six Orders may well have been derived 

 from a single ancestral Order characterised by the following- 

 points: presence of an aphantoneuric archedictyon, presence of 

 microtrichia all over the wing, and pi-esence of well-developed 

 macrotrichia upon the main veins and their branches, and upon 

 the archedictyon, but not upon the true cross-veins. 



Such a type is preserved in the fossil Archipanorpa from the 

 Trias of Ipswich, Queensland. This fossil itself, however, cannot 

 have been the ancestral form, since the Mecoptera, Trichoptera, 

 and Planipennia, at any rate, are contemporaneous with it, while 

 the first of these three Orders goes ])ack also into the Permian. 

 For the actual ancestor we must postulate some unknown type 

 of the Lower Permian, or possibly even of the Upper Carbon- 

 iferous; and whether this ancestor is to be considered as belong- 

 ing to the Protomecoptera or not, will have to depend upon 

 other characters not dealt with in this Part. 



Let us now follow the evolutionary changes of the various 

 structures of the wing separately. 



The Archedictyon : — This undergoes complete suppres- 

 sion in all recent Orders, except only in a few Lepidoptera, where 

 distinct traces of the mesh work in an aphantoneuric condition 

 (but not so well marked as in Archipanorpa) are still to be found. 

 This is well shown above the radius in the forewing of Proto- 

 tkeora pHrosema Meyr. (Text-fig.34, and Plate Ixviii., tig. 1 I). 



