Fig. 8. Dopamine stimulation causes secretory vesicle loss and appearance of vacuoles. Cyprids were fixed at different times during exposure to dopamine (1 mmol l^–1) and sectioned. Sections were stained with Toluidine Blue, and the different types of vesicles in the stained sections were counted under the microscope. Note that dense-core granules (type 1) reduce in number over time, with a proportionate increase in the number of vacuoles (type 4) after 10 min of dopamine treatment.