In Callinectes sapidus (Blue Crabs) the excretory system consists of two soft, grayish or pale greenish-white antennal glands. These two antennal glands are found within the anterior wall of the cephalothorax behind the second antenna and are saccate nephridia that include an end sac that originates from the coelom as well as a tubule and labyrinth that stem from its coelomoduct. Across the walls of the end sac the ultrafiltration of the blood occurs and the labyrinth modifies the filtrate. The final urine is stored in two very large transparent, thin-walled bladders, which are emptied into the exterior by the nephridiopores on the peduncle of the first antenna.