ITS OUTER SKELETON. 61 



joints bear numerous fine but stiff hairs upon the walking 

 surface. The extremity of the fifth joint is segmented off, and 

 carries a pair of equal and strongly curved claws,* 



At the base of each leg are several chitinous plates (fig. 28), 

 upon which no small labour has been bestowed by different 

 anatomists. They are arranged so as to form two joints inter- 

 mediate between the coxa and the sternum, and these two joints 

 admit of a hinge-like movement upon each other, while their 

 other ends are firmly attached to the coxa and sternum respec- 

 tively. (Compare III and IIL\, fig. 28.) These parts in the 

 Cockroach may be taken for two basal leg-joints which have 

 become adherent to the thorax. In other cases, however, they 

 plainly belong to the thorax, and not to the leg. In the Mole- 

 cricket, for instance, similar plates occur ; but here they are 

 firmly united, and form the lateral wall of the thorax. In the 



*> 



Locust they become vertical, and lie one in front of the other. 

 Most authors have looked upon them as regular elements of a 

 typical somite. They regard such a segment as including two 

 pleural elements viz., a dorsal plate (epimeron), and a ventral 

 plate (episternum). We have already (p. 34) given reasons for 

 doubting the constancy of the pieces so named. It is not 

 inconvenient, however, to denote by the term episternum the 

 joint which abuts upon the sternum ; for the joint which is 

 applied to the coxa no convenient term exists, and its occurrence 

 in Insects is so partial, that the want need not be supplied at 

 present.f Both joints are incompletely subdivided. In the first 

 thoracic segment of the Cockroach they are less firmly con- 

 nected than in the other two. 



Cockroaches of both sexes are provided with wings, which,, 

 however, are only functional in the male. The wing-covers (or 

 anterior pair of wings) of the male are carried by the second 

 thoracic segment. As in most Orthoptera genuina, they are 

 denser than the hind wings, and protect them when at rest. 

 They reach to the fifth segment of the abdomen, and one 



* Professor Huxley (Anat. Invert. Animals, p. 404) points out that the so-called 

 pulviUus ought to be counted as a sixth joint. The same is true of the foot of 

 Diptera and Hymenoptera, where there are six tarsal joints, the last carrying the 

 claws. (Tuff en West on the Foot of the Fly. Linn. Trans., Vol. XXIII.) 



t The nomenclature adopted by Packard (Third Report of U.S. Entomological 

 Commission) seems to us open to theoretical objections. 



