The symbolic and subsymbolic paradigms each offer advantages and disadvantages in constructing models for understanding the processes of cognition. A number of research programs at U C L A utilize connectionist modeling strategies, ranging from distributed and localist spreading-activation networks to semantic networks with symbolic marker passing. As a way of combining and optimizing the advantages offered by different paradigms, we have started to explore hybrid networks, i.e. multiple processing mechanisms operating on a single network, or multiple networks operating in parallel under different paradigms. Unfortunately, existing tools do not allow the simulation of these types of hybrid connectionist architectures. To address this problem, we have developed a tool which enables us to create and operate these types of networks in a flexible and general way. W e present and describe the architecture and use of DESCARTES, a simulation environment developed to accomplish this type of integration.