The development of the visual cortex in the rat was studied in animals from embryonic day El6 to postnatal day P28. Five lectins (WGA, sWGA, PNA, PHA-E, and Son-A) were used to probe the molecular basis of development in terms of glycoconjugates. Alcian blue was used to determine the ontogeny of extracellular matrix glycosaminoglycans (GAGs). The developmental role of succinate dehydrogenase, cytochrome oxidase, and ot-naphthyl acetate esterase was studied. The pattern of lectin binding reflected a programmed dynamic spatio-temporal process in the expression of glycoconjugates that was concluded by PI 5. Sialic acid and an extended sugar specific for PHA-E were important for dendritic arborization and synapsing. N- cetylgalactosamine / galactose served a barrier function for the growth of neuronal processes. Established dendrites expressed sugar moieties of the mannose-glucose type N-acetylglucosamine had a role in vasculogenesis. Using alcian blue, hyaluronic acid and sulfated GAGs were demonstrated in the extracellular matrix during development. Their disappearance from the extracellular compartment followed an inside-out sequence that was culminated by PI5. A proposal that glycoconjugates participate in the formation of a morphogenetic field during development was contemplated. Enzymes reflected a heterogeneous spatio-temporal expression in the visual cortex during development. Succinate dehydrogenase was strongly and differentially expressed since prenatal stages. A mature band of activity in lamina IV was attained on PI 5. Cytochrome oxidase expressed a weak activity between PI-P20. A mature band of strong activity in lamina IV appeared suddenly on P21. The heterogeneous expression of oxidative enzymes during development was discussed from a biochemical and evolutionary point of-view. Esterases, as demonstrated by the simultaneous azo coupling method using a-naphthyl acetate, were different from acetylcholinesterase. The non-specific esterase activity was expressed in an inside-out pattern until PI5. A role for non-specific esterases in the degradation of neurofransmitter(s) other than acetylcholine was discussed. Most of the morphogenetic events were culminated by PI5 and followed an inside-out thumbprint. This spatio-temporal scheme was not perturbed by blinding at birth. An elementary cusp model of development of the visual cortex was synthesized in view of the catastrophe theory.