Fig. 90.—Transverse section of Ab­do­men, Lamelli­corn Beetle. The posi­tion of the terga and sterna after an in­spir­ation, is in­dica­ted by the thick line; the dot­ted line shows their posi­tion after an ex­pir­ation, and the arrow marks the direc­tion of the ex­pir­atory move­ment.

Fig. 91.—Transverse section of Abdomen, Cock­roach (P. orient­alis).

In the Cockroach (Periplaneta) the sterna are slightly raised during expiration. (See figs. 89 and 91.)

(b) Terga well developed, overlapping the sterna on the sides of the body, and usually concealing the pleural membrane, which forms a sunk fold. The terga and sterna approach and recede alternately, the sterna being almost always the more mobile. To this type belong Odonata, Diptera, aculeate Hymenoptera, and Acridian Orthoptera. (Fig. 92.)

(c) The pleural membrane, connecting the terga with the sterna, is well developed and exposed on the sides of the body. The terga and sterna approach and recede alternately, while the pleural zone simultaneously becomes depressed or returns to its original figure. To this type the writer assigns the Locustidæ, the Lepidoptera and the true Neuroptera (excluding Phryganidæ). (Fig. 93.)