A cell biological study of the micropylar apparatus in dipterans of economic importance

Abstract

The micropylar apparatus is a specialized region of the eggshell, serving as a passage (micropylar canal) to the spermatozoon. The entire eggshell is secreted by the follicle cells during oogenesis, in successive layers, in the following order: vitelline membrane, wax layer, innermost chorionic layer, endochorion, exochorion. This study is an E.M. investigation of the structure and morphogenesis of the micropylar apparatus at the follicles of Dipterans of economic importance, such asCeratitis capitata,Dacus oleaeandRhagoletis cerasi. These insects affect the fruits of orange, olive and cherry trees respectively.The micropylar apparatus of the DipteransC. capitata,D. oleaeandR. cerasi. forms a protrusion at the anterior part of the egg. This apparatus consists of the vitelline membrane (Vm), which is surrounded by the wax layer (wl); the innermost chorionic layer (icl); the endochorion (En); and the exochorionic “tuft”. The endochorion has many cavities which probably take part in the air storage, in order to facilitate the embryo’s respiratory needs (Figs. 1,3,5). The micropylar canal is covered by the characteristic tuft, resulting in the vitelline membrane, where it becomes thinner and forms the pocket.