212 



THE COCKROACH 



curious is that the latter type has been found only in the New 

 World, while the former is common to Europe and America. 

 The latter appears to be the more archaic type, since it is 

 probable that the primeval Insect wing was broad at the base, 

 as is the general rule in palaeozoic wings, and had the veins 

 somewhat symmetrically disposed on either side of a middle 

 line ; in this case the mediastinal and anal areas would be 

 somewhat similar and more or less triangular in form, and the 



Fig. 121. Mylacris anthracophilum Scudd. X 2. Carboniferous, Illinois. 



space they occupied would be most readily filled by radiating 

 veins ; such a condition of things, which we find in the 

 Mylacridce, would naturally precede one in which the mediastinal 

 vein, to strengthen the part of the wing most liable to strain, 

 should, as in the Blattinarice, follow the basal curve of the 

 costal margin, and throw its branches off at intervals toward 

 the border, much after the fashion of the mediastinal vein. 



This view of the relative antiquity of the two tribes of 

 PalcBoblattaricB is supported by the fact that while in both of 

 them the internomedian branches show a tendency to repeat 

 the general course of the anal nervules, as in the corresponding 

 veins of the costal region, this tendency is lost in modern types ; 

 and among those ancient Blattinarice, which are esteemed 

 highest in the series, there is a marked tendenc}^ toward a loss 



