Ink of cuttlefish is a substance released by cuttlefish when it escapes from danger. It is rich in protein and rich in nutrition. At the same time, cuttlefish juice is also rich in mucopolysaccharide, which is one of the important components of human bones, blood vessels and skin.

Squid ink is synthesized by the secretory glands in the ink sac, stored in the ink sac, and sprayed through the rectum and anus when encountering enemies. Ink sac is a very developed rectal blind sac, which is located on the posterior ventral side of visceral mass. The front end is a slender tube, Jimo sac tube, which communicates with rectum near anus, and there are two groups of annular sphincter muscles near the opening. Because the amount of ink stored in the ink bag is uncertain, its shape and size change greatly.