I 



IX COCKROACHES 223 



cases it is so obscure externally as to leave its existence in some 

 doubt. 



The sterna in Blattidae are remarkable for their rudimentary 

 structure. This is probably correlated with the great develop- 

 ment of the coxae, which serve as shields to the lower part 

 of the body. The pieces of the sterna are not only small, but 

 are also of feeble consistence semi-membranous, in fact and 

 appear like thicker portions of the more extensive and delicate 

 membrane in which they are situate ; they sometimes differ 

 considerably in the sexes of the same species. The coxae have 

 very large bases, and between them and the sterna are some 

 pieces that are grooved and plicate, so that it is not easy to 

 decide as to their distinctions and homology (Fig. 120). The 

 second breathing orifice is a slit placed in a horny area in the 

 membrane between the middle and hind coxae. 



The legs are remarkable for the large and numerous spines 

 borne by the tibiae, and frequently also by the femora : 

 the trochanters are distinct and of moderate size ; the 

 tarsi are five - jointed, frequently the basal four joints are 

 furnished with a pad beneath ; the fifth joint is elongate, 

 bears two claws, and frequently between these a pro- 

 jecting lobe or arolium ; this process scarcely exists in the 

 young of Stylopyga orientalis, the common cockroach, though 

 it is well developed in the adult. The hind body or abdomen 

 is ahvays large, and its division into rings is very visible, but the 

 exact number of these that can be seen varies according to age, 

 sex, species, and to whether the dorsal or ventral surface be 

 examined. The differences are chiefly due to the retraction and 

 inflexion of the apical segments ; the details of the form of these 

 parts differ in nearly every species. It is, however, considered 

 that ten dorsal and ventral plates exist, though the latter are 

 not so easily demonstrated as the former. The basal segment is 

 often much diminished, the first dorsal plate being closely con- 

 nected with the metanotum, while the first ventral may be still 

 more rudimentary ; much variety exists on this point. In the 

 female two of the ventral terminal plates are frequently inflexed, 

 so as to be quite invisible without dissection. From the sides of 

 the tenth segment spring the cerci, flat or compressed processes 

 very various in size, length, and form, usually more or less 

 distinctly jointed. Systematists call the seventh ventral plate of the 



