THE COCKROACH I 



All the terga are dense and opaque in the female ; in the 

 male the middle one (mesonatmri) and the hindmost (mctano- 

 tum) are thin and semi-transparent, being ordinarily overlaid 

 by the wing-covers. While the thoracic terga diminish back- 

 wards, the sterna increase in extent and firmness, proportionally 

 to the size of the attached legs. The prosternum is small and 

 coffin-shaped ; the mesosternum partly divided into lateral 

 halves in the male, and completely so in the female. The 

 metasternum is completely divided in both sexes, while a 

 median piece, carrying the post-fiirca, intervenes between its 

 lateral halves in the male. Behind the sterna, especially in the 



Fig. 27. Ventral Plates of Neck and Thorax of Male Cockroach. 

 I, prosternum ; II, mesosternum ; III, metasternum. X 6. 



case of the second and third, the flexible under-surface of the 

 thorax is inclined, so as to form a nearly vertical step. In the 

 two hinder of these steps a chitinous prop is fixed ; each is 

 Y-shaped, with long, curved arms for muscular attachment, and 

 a central notch, which supports the nerve-cord. The hind- 

 most of these, known as the post-furca, lies immediately behind 



