Squids excrete ink and wastes from digestion. A squids body is basically inside a "sack" called the mantle which gives it the arrowhead or spearlike shape. Squids seem to be backwards in appearance and movement. At one end are the 10 arms or tentacles, the tentacles are attached to the head, in the center of the tentacles is the mouth with two hard sharp beaks.The head looks like it is poking out of that sacklike mantle. The alimentary canal leads from the mouth towards the pointy end of the squid where the stomach is. Squids swim around stomach first with the head at the back looking to see where it's been.Perhaps they are more interested in the past than the future. Anyway, from the stomach the digestive track runs back towards the head end, the anus empties into the siphon. The siphon is a powerful muscular tube that runs along the "underside" of the body inside the mantle, the mantle and the siphon pump water through it from the "pontedy end" to the opening under the head. The squid can shoot a powerful stream out the siphon and jet propell itself through the water up large squid up to 50 mph, 1 inch squid can rocket out of the water to heights of 12 feet! . Up stream from the anus in the siphon are the gills, that's how the squid breathes. The anus excretes into the siphon and the siphon pumps or even shoots the waste out. A tube runs from the ink sack, just behind the head to the digestive track just before the anus. The ink sac produces the ink which is mostly melanin, the dark pigment common to all animals including us people, and some enzymes, and gelatinous protein like material, or mucous. The ink sack is powerful enough to push ink into the siphon which can shoot it out like a jet engine. The mucous hold the ink together enough to confuse a predator as the squid rockets away. The enzmes alert other squid that danger is near and they all go shooting off.