Fig. 4. Electron microscopy of cement glands in (A) control, unstimulated cyprids and (B) cyprids stimulated with 1 mmol l^–1 dopamine for 10 min. The different types of granules are labelled in B and can be compared with Fig. 2. In control, unstimulated animals, most of the granules are type 1, but all the four types of granules are visible in stimulated cement glands (B). Note also that the different types of granules are within the same cell in B. Scale bar: 3.8 µm in A; 2.5 µm in B.