With larger vesicles and thicker vesicle walls, scoria sinks rapidly. The Arp2/3 complex also regulates the intracellular motility of endosomes, lysosomes, pinocytic vesicles, and mitochondria. Retrieval of synaptic vesicles occurs by endocytosis. Melanocytes insert granules of melanin into specialized cellular vesicles called melanosomes. Microtubules function as tracks in the intracellular transport of membrane-bound vesicles and organelles. Transport occurs via vesicles and monomeric transport in the cytosol. Fimbriae are also responsible for invasion of membrane vesicles into host cells. The release of neurotransmitter vesicles from the presynaptic cell is probabilistic. This vaccine was based on artificially produced outer membrane vesicles of the bacterium. The virus acquires its final envelope by budding into cytoplasmic vesicles. The empathogen-entactogen MDMA releases serotonin from synaptic vesicles of neurons. This appearance is due to a high concentration of vesicles and vacuoles. Semen is produced in the seminal vesicles, prostate gland and urethral glands. Microtubules are also required for the trafficking of membrane vesicles. Splits or pockets may form in the germinal sheet of cells forming vesicles or elongations.