Ultrastructure and development of the extensible abdominal intersegmental membranes of the female migratory locust

The cuticle of the retracted extensible membrane of the female locust is 300 microm thick and below its highly folded epicuticle there is a zone (5 microm thick) of helicoidally oriented laminae of microfibrils (lamellae), an elastomer layer (180 microm thick) of microfibrils with no preferred orientation and a subcuticular zone (1 microm thick). The epidermal cell layer has an extensive system of junctional specializations and pore canals traverse the cuticle to the helicoidally oriented lamellae. In the newly ecdysed adult the elastomer layer is absent and the helicoidally oriented lamellae are incomplete. Essentially the membrane consists of an elastomer layer contained between two stable layers cross-linked by pore canals, one to the other. When in the plasticized state the membrane combines low stiffness with high extensibility and during extension the elastomer layer flows. Recovery is effected by muscles and when the two stable layers have returned to their unstretched states the fluid elastomer is again evenly distributed. There is an increase in the water content and in the volume of the cuticle when it is fully extended. The ultrastructure of the extensible membrane is compared with those of the inextensible membranes from male and female locusts.