310 Sellards — Structural Characters of Cockroaches. 



who from illustrations alone compared the fossils with some 

 coleopterous larvae, and at the same time called attention to 

 their striking resemblance to the nymphs of cockroaches.* 



Beecher, although his results were not published, recognized 

 Dipeltis as a nymph cockroach, and made plaster casts of liv- 

 ing nymphs to show the close similarity. Over fifty specimens 

 of nymphs cockroaches in various stages of development have 

 now been obtained, and these have been very useful in the 

 present study. 



Structure. 



Although the modern cockroaches are comparatively gen- 

 eralized insects, yet in important respects their Paleozoic 

 ancestors were of a much more generalized structure, the adults 

 retaining some characters now to be seen in the nymph stages 

 only. The most marked changes since Paleozoic time have 

 occurred in the front and hind wings, the abdomen, and the 

 ovipositors. 



Front Wings. — The tegmina have been thoroughly studied 

 by Scudder and others, and compared with the front wings of 

 living cockroaches.f 



Hind Wings. — The more delicate hind wings are rarely 

 preserved, but a considerable number have been obtained, 

 especially from the Kansas deposits. The costal border is 

 nearly straight, or often a little concave in the proximal half 

 and rounded to the apex in the distal half (Plate YII, figure T). 

 The anal area was not so largely developed and, as Scudder 

 has noted, did not possess the fanlike plaiting seen in almost 

 all modern cockroaches.^ 



The longitudinal fold between the cubital and anal areas, 

 which is common to the recent cockroaches, does not seem to 

 have occurred in any of the Paleoblattidse. Several specimens 

 are now known with the wings still in their natural position 

 over the abdomen. In all of these cases, and also when found 

 detached, the wings are always spread full width. It should 

 be added, however, that a large undescribed species in the 

 writer's possession, from the Upper Coal Measures, presents 

 some indications of the doubling under of a part of the anal 

 area, but in no instance is the fold between the cubital and 

 anal veins. The main veins of the hind wing are more evenly 

 developed than in most of the living forms. The first main 

 vein, or costa, which is simple and usually marginal in the 

 adult condition of living insects, is not only some distance from 

 the margin, but in the more primitive Mylacridse, and occasion- 

 ally in the Blattinarise, gives off a few superior branches. This 



* Natural Science, vol. xii, p. 42, January, 1898. 



f Mem. Boston Soc. Nat. Hist., vol. iii, pp. 23—184, 1879, and elsewhere. 



% Mem. Boston Soc. Nat. Hist., vol. iii, p. 322, 1885. 



