r»v II. 



TILLYARD. 



0-27 



a. 



d. 



about 30/x, lint in most cases lio between 10/x and 20/x. Similar 

 hairs are frequently present upon the softer parts of the bod}-, 

 as, for instance, on the abdominal sutures and pleurto. (Text- 

 fig. 17, a, cZ). 



Macrofrichia (Gr. fiaKpo^, large; and Opi^) are much larger 

 and stronger hairs, much less abundant, and oidy developed from 

 large specialised hypoderm-cells (trichogen cells) in connection 

 with special nerve-endings. They are thus of the nature of 

 i^ptisillfp, and homologous with similar hairs on othei* parts of the 

 body. Their bases of insertion are in the 

 form of raised circular rings, enclosing an 

 opening in the cuticle, which is continued as 

 a very definite lumen within the hair, almost 

 to its very tip. These hairs are almost uni- 

 versally present upon the main veins and 

 their branches, less frequently upon the 

 membrane of the wing, and only in very 

 special cases upon the true cross-veins. In 

 several Orders they become evolved, in cer- 

 tain cases, by a process of flattening, into 

 scales; but this development is only spasmodic 

 except in the Order I.epidoptera, where scales 

 are found universally. (Text-fig. 17,6, c, e,/). 



Those macrotrichia found upon the veins 

 are usually somewhat larger and stronger than those found upon 

 the membrane, and both series may vary c(msiderably in size 

 upon the same wing. In different insects, the limits of variation 

 of these hairs may be placed at from 40/x to over 200/x. Text- 

 fig. 17 shows two sets of fairly normal hairs, one from Panorpa, 

 and one from Rhyphus. 



It is the purpose of this Part to study the evolution of the 

 Wing-Trichiation in the various Orders of the Panorpoid Com- 

 plex. As this is partly dependent upon the state of evolution of 



* Hairs from the wings of Panorpa confitsa VVestw., (a-c), and Rhyphus 

 brecis WaAk., {d-f); a, d, microtrichia; b, e, macrotrichia from wing-mem- 

 brane; f, /, ditto, from main veins; ( x 375). 



a (U) 



h ^ I 



c. e. 



Textfiir.l'; 



f. 



