246 POPULAR SCIENCE MONTHLY 



given off which strengthen the upper edge of the wing. The following 

 vein, the radius, reaches as a rule to the apex, and its branches given 

 off from the upper side fill the apex. The medius, which is often of 

 lesser importance, terminates on the inner border not far from the apex, 

 and gives off a few usually superior branches. The fifth vein of the 

 wing, the cubitus, is of more importance. It reaches along the inner 

 border of the wing one half to two thirds the distance towards the apex, 

 giving off strong inferior branches which strengthen the lower edge 

 of the wing. The remaining small area on the lower inner corner of 

 the wing is marked off by a deep furrow. The veins of this area are 

 all simple or once forked, and pass with a uniform curve from their 

 origin to the inner border. 



The next type (Fig. 2) is from later deposits — the Permian. Here 

 two of the main veins, the radius and media, have become fused for a 

 little distance from their origin, so that instead of four strong veins 

 arising from the middle of the base there are here only three. Other- 

 wise the wing is not unlike the Coal Measure form. Many of the 

 mesozoic wings have, in addition to a partial fusion of two or more 

 of the main veins, a further radical change in the anal area, the veins 

 of which, instead of ending on the inner border, run to and end on 

 the anal furrow. The front wing of one of the living cockroaches, the 

 common ' croton bug,' is shown in figure 3. Here cross veins are 

 numerous, and the anal veins, as in most of the Mesozoic forms, end 

 on the anal furrow. The wings described are those which are in a gen- 

 eral way typical of their time. Along with each of these are found 

 wings, some of which are more advanced, while others are of more 

 simple structure than those illustrated. Among modern cockroaches 

 not a few genera and species have both front and hind wings so incom- 

 pletely developed as to be entirely useless, and present only as function- 

 less wing pads. All Paleozoic cockroaches, so far as known, were pro- 

 vided with fully developed functional wings, the modern wingless forms 

 having descended without doubt from winged ancestors. 



The hind wings of Carboniferous cockroaches are as a rule broad 

 with rounded inner border; the veins are evenly distributed; there 

 are no cross veins; no indication of any fan-like plaiting such as is 

 found in the hind wings of modern forms; apparently there was no 

 folding, the wing lying spread out across the abdomen. Neither is 

 there any differentiation into a thicker, brownish, outer part, and a 

 thinner, membranous folded part. The hind wing, being less firm 

 than the front, is naturally less often preserved. Nevertheless a con- 

 siderable number have now been obtained. In the structure of the 

 hind wing the Carboniferous cockroaches present fairly uniform char- 

 acters, only occasionally, and from late Carboniferous deposits, are 

 there indications that a folding of the wing had originated. 



