Fig. 3. Ink visualization of the jets generated by the crayfish fan organs. Bilateral jets directed at 25° and 40° upwards (A) and horizontally (B); unilateral jet directed horizontally (C). Water-based ink for a fountain pen was used. After the animal had been observed fanning for about 1 min, the ink was slowly released from a pipe of 0.6 mm i.d. placed in front of the animal fan organs. Caution was taken to prevent the ink from getting in contact with the animal's chemoreceptors. The photo in A was acquired 5 s, and in B and C, 30 s, after the beginning of the ink injection.