Chap. XIII.] THE COCKROACH. 261 



being divided into two lateral halves, and is so divided in the 

 female. The metasternum is the largest of the three sterna, and 

 is in both sexes completely divided into two lateral divisions, 

 between which is wedged in the base of a Y-shaped chitinous 

 prop (post-furca) for the support of the nerve-chain and for 

 attachment of muscles. A similar prop (medi-furca) is connected 

 with the mesosternum. An anti-furca is, if at all, incompletely 

 represented. 



Each somite of the thorax carries a large pair of legs, of 

 which the anterior are the smallest, the posterior the largest. 

 Like those of the crayfish, they are jointed (arthropod type) ; 

 the divisions being coxa (proximal), trochanter, femur, tibia, and 

 tarsus, composed of six joints (or five joints, the last being sub- 

 divided). The distal division of the tarsus bears claws or 

 ungues (80, C.). 



The limbs do not articulate directly with the sterna or nota, 

 two lateral pieces intervening. These are shown in 80, C. One 

 of these (a) is, in the third limb, triangular, and is attached to 

 the coxa. The other (b) is larger, and curves round the angle 

 of a. It articulates, on the one hand, with the sternum (st.), 

 and on the other with the notum (no.). This latter piece (b) 

 seems, in the cockroach, to belong to the somite ; the former (a) 

 to the appendage. But there is some doubt about the homo- 

 logies of these parts in the insecta. 



Male cockroaches have, when adult, two pairs of wings. The 

 anterior (wing-covers or tegmina) are brown and stiff, and 

 attached to the second thoracic segment; the posterior pair, 

 attached to the metathorax, are soft and membranous, and, 

 when not used in flight, carried folded up beneath the wing- 

 covers. Both tegmina and wings are strengthened by nervures, 

 united by transverse ridges. The disposition of the nervures 

 will be readily seen with the aid of a lens. It is a matter of 

 importance in the classification of these and allied insects. The 

 old-world cockroaches seem to have had transparent mem- 

 branous wing-covers or anterior wings. 



In the female the wings remain in a rudimentary condition. 

 The anterior pair (wing-covers) are small, not reaching beyond 



