PHYLOGENY 



99 



than with any other order. Possibly they arose as offshoots of 

 some early Psocopterous group, but evidence of this contention is 

 not forthcoming. 



The oldest order of the Holometabola are the Mecoptera which 

 were already well represented in Lower Permian times. The 

 venation of these early Mecoptera (Fig. 48, A), however, is so 

 fundamentally different from either that of the Palaeodictyoptera, 

 or of the Protorthoptera, that we are led to the conclusion that 



2-5 



Fig. 48. A, Permochorista jucunda Till, fore wing. x 6-5. 

 B, Belmontia mitchelli. Till, x 2-5. (Adapted from Tillyard.) 



a long series of transitional forms must have existed in early 

 Carboniferous times, of which we have as yet no evidence. 

 Although its ancestry is, therefore, obscure, the order itself is 

 of great phylogenetic importance, since all the main groups of 

 the Holometabola (excepting the Coleoptera and Hymenoptera) 

 are perhaps referable to a Mecopterous ancestry The extinct 

 sub-order Protomecoptera, with its tendency to a more profusely 

 branched venation and the widened costal space, included Merope- 

 like forms which may well have been ancestral to the Neuroptera. 

 The sub-order Paramecoptera (Fig. 48, B) of the Upper Permian 



