Structure and formation of the chorion in the butterfly, Calpodes

The hemispherical eggshell of Calpodes consists of a domed dorsal surface of thin inner endochorion and a thick, lamellate, outer exochorion, and a flat bottom of predominantly unlamellated endochorion. The endochorion is traversed by small pores and the exochorion by larger ones, which are formed by the withdrawal of processes from the follicular cells. The presence of a phenoloxidase in the ovariolar ducts, lateral and common oviducts and in ovulated eggs, and the stability of ovulated eggs suggest that stabilization of the eggshell is accomplished through quinone tanning. However, the endochorion, which is soluble in sodium dodecyl sulphate (SDS), is more likely cross-linked by di- and tri-tyrosyls through the action of a peroxidase, present in the cells of the ovariolar duct and in the endochorion.