1938] 
Lines of Descent of Insects 
177 
Corydalid Neuroptera is rather suggestive of that of certain 
Protoblattid Protorthoptera. The venation of the Protor- 
thopteroid insect Metropator (which is regarded as a 
“Palseodictyopteroid” insect by Handlirsch) exhibits certain 
features suggestive of the precursors of the Sialid type of 
venation, but Metropator is an oligoneurous form (with few 
veins) and it is hardly probable that the more richly veined 
(polyneurous) types of Neuroptera, especially the fossil 
forms, were derived from the oligoneurous Metropator type 
of Protorthopteroid insect. In fact, it is very probable that 
the Protorthopteroid ancestors of the Neuroptera were both 
oligoneurous and polyneurous, and both tendencies would 
naturally reappear in their Neuropterous descendents if 
both tendencies occurred in the ancestral stock. Some in- 
vestigators consider that the venation of the Neuroptera 
indicates that they were derived from Palseodictyoptera, but 
the Neuroptera are clearly Neopterygota capable of laying 
the wings back along the body in repose, and their larvae 
intergrade extremely closely with those of the Coleoptera, 
clearly indicating that the Neuroptera were derived from 
the same Protorthopteroid ancestors as the Coleoptera, and 
the venation of the primitive Neuroptera might readily be 
derived from the type exhibited by certain Protoblattid 
Protorthoptera. 
The Mecoptera are extremely closely related to the 
Neuroptera, and were evidently derived from the same 
Protorthopteroid ancestors from which the Neuroptera 
were descended. The venation of the primitive Mecoptera 
suggests that their ancestors were similar to the Protoblattid 
Protorthoptera in certain respects, although Tillyard con- 
siders that the Mecoptera were derived from ancestors of 
the Metropator type, and Tillyard likewise considers that 
the Mecoptera are more primitive than the Neuroptera. 
The head and mouthparts of the Mecoptera are more spe- 
cialized than those of the Sialid Neuroptera, however, and 
the thoracic sclerites of the Neuroptera are of a much more 
primitive type than those of the Mecoptera, while some 
Neuroptera such as Raphidia have retained an Orthopteroid 
ovipositor which is lost in typical Mecoptera, so that the 
Neuroptera are more primitive, in general, than the Mecop- 
tera are, and have departed less than the Mecoptera have, 
