none Alysia manducator; ENDOCRINE-SYSTEM; Neurosecretory system function; LARVAL-DEVELOPMENT; Diapause onset & neurosecretory system function; DIAPAUSE-; Larva, effect of temperature; TEMPERATURE-; Larval diapause & neurosecretory system function relationships Development of Alysia manducator larvae is regulated by temperature. Low temperature (5-12 degree C) causes cold, and high ones (25-27 degree C) - heat diapause. Active development is possible only at 18-23 degree . Neurosecretory system of the larvae was investigated during reactivation at 12 degree C after heat diapause and also after transfer of the larvae diapausing at 5 degree C to 27 degree C. Drop of temperature from 27 degree C to 12 degree C removes quickly the block that inhibited the development at 27 degree C and the neurosecretory material accumulated in the course of the heat diapause is released to haemolymph which results in the morphogenesis. When the diapausing larvae were transferred from 5 degree C to 27 degree C, functioning of the neurosecretory system was re-arranged within two days stay under new conditions irrespective of the duration of the residence at coldness. As in the previous case, the process starts with the release of the accumulated neurosecretory material. As opposed to the reactivation, when this process is irreversible and results in morphogenesis, at high temperature the process is ceased soon after the beginning, and the accumulation of the neurosecrete, typical of the diapause, is rapidly restored. Prompt replacement of the partial activation by the onset of new diapause presumes an activity of the inhibitory factor. Distinct correlations between the external reaction of the individual and the state of the median neurosecretory cells of the brain have been revealed.