Final answer:
The green gland is the organ in crayfish responsible for excreting wastes near the base of the antenna, functioning as part of the crayfish's excretory system.
Step-by-step explanation:
The organ in crayfish that functions to excrete wastes near the base of the antenna is called the green gland. In arthropods like the crayfish, the green glands are excretory organs that filter waste from the blood, concentrate it, and then excrete it through a pore close to the base of the antennae. This is different from annelids and insects, which utilize nephridia and Malpighian tubules, respectively, for their excretory processes. The green gland is crucial for maintaining the internal balance of water and salts, which is vital for the crayfish's survival in aquatic environments.