Family _Blattina_. Body usually depressed, oval. Pronotum shield-like. Legs adapted for running only. Wing-covers usually leathery, opaque, overlapping (if well developed) when at rest, anal area defined by a furrow (fig. 4). Head declivent, or sloped backwards, retractile beneath the pronotum. Eyes large, ocelli rudimentary, usually two, antennæ long and slender. [Illustration: Fig. 4.--Generalised sketch of Cockroach wing-cover.] About eight hundred species of Cockroaches have been defined, and to facilitate their arrangement, three groups have been proposed, under which the different genera are ranked.[13] Group 1. Both sexes wingless (_Polyzosteria_). Group 2. Males winged, females wingless (_Perisphæria_, _Heterogamia_). Group 3. Both sexes with more or less developed wings (about 7 genera). [13] For descriptions of the species Fischer’s Orthoptera Europæa (1853) or Brunner von Wattenwyl’s Nouveau Système des Blattaires (1865) may be consulted. The classification adopted by the last-named author is here summarised. BLATTARIÆ. A.--Femora spinous (_Spinosæ_). Fam. 1.--_Ectobidæ._ Seventh abdominal sternum undivided in female. Sub-anal styles absent in male. Wings with triangular apical area. _Ectobia_, including _E. lapponica_ (_Blatta_) and other genera. Fam. 2.--_Phyllodromidæ._ Seventh abdominal sternum undivided in female. Sub-anal styles usual in male (0 or rudimentary in _Phyllodromia_). Wings without triangular apical area. _Phyllodromia_, including _P. germanica_ (_Blatta_) and other genera. Fam. 3.--_Epilampridæ._ Fam. 4.--_Periplanetidæ._ Seventh abdominal sternum divided in female. Sub-anal styles conspicuous in male. _Polyzosteria_, _Periplaneta_, &c. B.--Femora not spinous (_Muticæ_). Families.--_Chorisoneuridæ_, _Panchloridæ_, _Perisphæridæ_, _Corydidæ_, _Heterogamidæ_, _Blaberidæ_, _Panesthidæ_. Many useful references will be found in Scudder’s Catalogue of N. American Orthoptera, Smiths. Misc. Coll., viii. (1868). In Group 3 occur the only two genera which we shall find it necessary to describe--viz., _Blatta_, which includes the European Cockroaches, and _Periplaneta_, to which belong the Cockroaches of tropical Asia and America. Genus _Blatta_. A pulvillus between the claws of the feet. The seventh sternum of the abdomen entire in both sexes; sub-anal styles rudimentary in the male. Genus _Periplaneta_. Readily distinguished from Blatta by the divided seventh abdominal sternum of the female, and the sub-anal styles of the male. Two species of Periplaneta have been introduced into Europe. These are-- 1. _P. orientalis_ (Common Cockroach, Black Beetle). Wing-covers and wings not reaching the end of the abdomen in the male; rudimentary in the female. 2. _P. americana_ (American Cockroach). Wing-covers and wings longer than the body in both sexes. CHAPTER III.