Flame cells are scattered throughout parenchyma from which they remove metabolic wastes. A flame cell is of irregular shape, with granular cytoplasm and a nucleus. Bundle of cilia, or flame, arises from basal granules near nucleus. Cilia are enclosed into a funnel-shaped lumen formed by the terminal blind end of a capillary. Protonephridia are found in flatworms, Malpighian tubules in insects and green glands in crustaceans.

The excretory structures of flatworms, specifically Taenia, are flame cells. Flame cells are specialized cells that are responsible for excretion and osmoregulation in flatworms. They are found in the excretory system of these organisms.

Flame cells work by actively pumping excess water and waste products out of the body of the flatworm. They are named "flame cells" because of their unique appearance under a microscope. They have hair-like structures called cilia that beat rhythmically, creating a flickering flame-like appearance.

Flame cells are connected to a network of tubules called protonephridia. These tubules collect the waste products and excess water from the flame cells and transport them to the outside of the body. The protonephridia also play a role in maintaining osmotic balance within the flatworm's body.

The flame cells and protonephridia together form the excretory system of flatworms. This system helps remove metabolic waste products, regulate water and salt balance, and maintain homeostasis in these organisms.

Other excretory structures found in different organisms include malpighian tubules and green glands. Malpighian tubules are found in insects and some other arthropods, and they function in the excretion of nitrogenous waste. Green glands, also known as antennal glands, are found in crustaceans and play a role in osmoregulation and excretion.

In the case of flatworms, such as Taenia, flame cells are the primary excretory structures. They are well-suited for the simple body plan of flatworms and the relatively low metabolic rate of these organisms. Flame cells are an important adaptation that allows flatworms to efficiently eliminate waste and maintain proper water and salt balance.