Animals and plants possess hormones that trigger specific metabolic responses to environmental stimuli. Hormones contribute to the control of such essential activities as growth, water balance, and timing of the reproductive cycle. How land and freshwater gastropods regulate these activites is unknown: hormones have not been found. My objectives are to isolate, to identify, and to describe the mode of action of regulatory molecules that control the reproductive cycle of land and freshwater gastropods. (The land snail, Helix pomatia, will be used.) I have developed a bioassay which utilizes organ culture to detect a precise metabolic response of a target organ, the albumen gland, to the action of regulatory molecules. The albumen (egg white) gland synthesizes galactogen, a galactose homopolymer, in preparation for summer egg laying. In autumn, the gland instead accumulates glycogen as a food reserve for winter hibernation. Thus a clear-cut biochemical manifestation of the seasonal cycles of reproduction and hibernation occurs. Experimental activation of galactogen synthesis within a quiescent gland provides a bioassay for the regulatory molecules that turn on an essential element of the reproductive cycle. My experiments have shown that albumen gland explants are easily maintained in culture and that activation of galactogen synthesis occurs when explants are co-cultured with the brain from a reproductively active snail. The regulatory molecules may be neurohormones. To carry out may objectives as stated above I will combine the techniques of organ culture with that of fractionation of brain neurosecretions in order to: (1) isolate the neurosecretion that activates galactogen synthesis; and (2) determine which enzymes in the galactogen synthetic pathway are affected by the neurosecretion.