. Smithsonian miscellaneous collections. anterior and posteriorlips {c, d). The length of the slit is about mm. in the malegrasshopper, and about mm. in the female. The anterior lip (f)is a rigid elevation of the wall of the peritreme; its inner face issoft and deeply grooved parallel with the outer edge. The posteriorhp {d) is a weaker and freely-movable flap, but it has a sharp, I NO. 2 THORACIC MECHANISM OF A GRASSHOPPER—SNODGRASS IO3 strongly-sclerotized marginal band (e) which, when the spiracle isclosed, fits into the groove of the anterior lip. Tlie cleft of the first spiracle
. Smithsonian miscellaneous collections. anterior and posteriorlips {c, d). The length of the slit is about mm. in the malegrasshopper, and about mm. in the female. The anterior lip (f)is a rigid elevation of the wall of the peritreme; its inner face issoft and deeply grooved parallel with the outer edge. The posteriorhp {d) is a weaker and freely-movable flap, but it has a sharp, I NO. 2 THORACIC MECHANISM OF A GRASSHOPPER—SNODGRASS IO3 strongly-sclerotized marginal band (e) which, when the spiracle isclosed, fits into the groove of the anterior lip. Tlie cleft of the first spiracle opens into a shallow atrium fromwhich are given off two tracheae, a larger dorsal one (fig. 51 B, /)and a smaller ventral one (g). From without, therefore, the firstspiracle appears to have a double opening (A, /, g,). In some of theOrthoptera that have tympanal organs on the front legs, the tracheaof the ventral (or posterior) opening of the spiracle appears to havebecome specialized as an acoustic trachea since it goes only to the. 51.—First thoracic spiracle of Dissosteira. A, outer view of left spiracle. B, inner view of right spiracle, a, ventral lobeof peritreme; b, process of peritreme protecting spiracle from covering flap ofpronotum; c, anterior lip of spiracle; d, posterior lip of spiracle; e, hard edgeof posterior lip; /, dorsal trachea; g, ventral trachea; /;, internal lever of pos-terior lip forming a septum between the tracheae; i, head of lever on whichclosing muscle (/g) is inserted; /, ventral internal process of peritreme onwhich spiracular muscles arise; ni, external pit forming internal process /; Ptr,peritreme; yg, opening muscle; 80, closing muscle. front leg, where it branches into the two tracheae of the tympanalorgan. This fact led Graber to the conclusion that the double structureof the first spiracle in Orthoptera originated from the separation ofan acoustic trachea from the general respiratory tracheae of theprothorax. Carpentier (1924, 1925), h
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