TOXOCARA-CANIS - ULTRASTRUCTURAL ASPECTS OF LARVAL MOLTING IN THE MATURING EGGS

The morphology of the surface of Toxocara canis larvae, developing in the eggs to reach infectivity, has been studied for the first time at an electron microscopical level. In most 11-day and some 15-day eggs, the larvae are surrounded by two shed cuticles. The outer first shed c uticle is composed of two layers. The inner second shed cuticle is muc h thicker than the outer one. The presence of both shed cuticles indic ates that the larva has undergone two developmental stages in the matu ring egg. The larvae in most 15-day eggs are surrounded by one shed cu ticle composed of outer electron-dense and inner layers. This cuticula r sheath is identical with the described inner second shed cuticle, ex cept for its apparently reduced thickness. The infective larvae inside the 30-day eggs are enveloped by one cuticular sheath, derived from t he second moulted cuticle, and consisting only of a single layer. The findings are discussed with respect to data concerning the moulting pr ocess in other nematode species.