1. From November, 1948 through January, 1950 quantitative plankton collections were made at monthly intervals from nine stations along the west coast of Florida.2. Surface water temperatures and salinities were taken at each station. The warmest water temperatures were similar at all stations but the coldest water by several degrees was found at the Cedar Key station (3A).3. The inshore water at all stations showed reduced salinity. This was correlated with rainfall. The salinity increased from the inshore to the offshore stations.4. Three maturity stages were described for the chaetognaths based on development of testes and ovaries.5. The chaetognaths collected were: S. hispida, S. helenae, S. tenuis, S. enflata, K. pacifica. One of these, S. hispida, exists characteristically in dilute inshore water. S. helenae and S. enflata were normally absent at the inshore stations where S. hispida was abundant. They were most numerous at the C stations where the salinity of the water varied around 35°/00. S. tenui...