314 Sellards — Structural Characters of Cockroaches. 



genetic connection between the ancient and modern forms, the 

 one standing in direct ancestral relation to the other. The body 

 had essentially the same shape. The legs indicate the same 

 habit of locomotion. The broad pronotum was as characteristic 

 a feature of the Carboniferous as of the recent cockroach, and 

 formed quite as secure a shelter for the small retractile head. 

 The front wings had a similar arched form, and the anal area 

 was as well defined. 



In view of the fundamental and close relations, it seems evi- 

 dent that the Paleozoic and recent cockroaches constitute two 

 nearly related and intergrading groups of a single order 

 Orthoptera, or, more accurately, two stages in the evolution of 

 a single phyluin. Recent studies have brought to light some 

 "new structural differences separating the two stages, without, 

 however, impairing the evidence of their interrelation. On 

 the other hand, the discovery of a form in the Carboniferous 

 with anal veins ending on the anal furrow and with strong 

 cross veins tends to break down apparent differences. The 

 very late Paleozoic and early Mesozoic species, when better 

 known, may confidently be expected to furnish other inter- 

 grading characters. 



The venation of the immature wings of modern nymph cock- 

 roaches is very similar to that of Paleozoic adults.* The 

 modern nymphs thus present in their development an instruc- 

 tive recapitulation of ancestral characters. 



The long ovipositor of Paleozoic cockroaches apparently 

 indicates that a well-developed ovipositor is a primitive char- 

 acter of the Orthoptera, the reduction of this organ in the 

 modern Blattidse, like the characteristic egg case and genital 

 pouch, being an expression of a specialized condition of the 

 external genital organs. Some other families of the order, as 

 the Locustidse, are, as regards the ovipositor, less differentiated 

 from the original type than are the cockroaches. 



The plication of the anal area, so constant a feature of v the 

 hind wings of modern Orthoptera, is likewise, as Seudder 

 maintains, a comparatively recent acquisition. 



It is worthy of remark that the plication, as also the fold, of 

 the hind wing of cockroaches developed subsequent to their 

 differentiation as a distinct phylum. A comparatively broad 

 anal expanse creating the need of a plication was,, however, 

 doubtless common to the early Orthoptera, but both the plica- 

 tion and the fold have originated independently in more than 

 one division of the order. The same is true of cross veins. It 

 is probable that at the time cockroaches were differentiated, 



* Compare, for instance, the venation of the wing of a typical Paleozoic 

 adult cockroach with that of recent nymphs, as given by Packard (Text 

 Book of Entomology, p. 138, 1898 ; or, Comstock and Needham, Amer. Nat., 

 vol. xxxiii, p. 574, 1899). 



