(a) Amphioxus is an example of a chordate that has flame cells as excretory structures. Flame cell is a type of excretory and osmoregulatory system.
(b) The cortical portions projecting between the medullary pyramids in the human kidney are the columns of Bertini. They represent the cortical tissues present within the medulla.
(c) A loop of capillary that runs parallel to Henleâ€™s loop is known as vasa rectae. Vasa rectae, along with Henleâ€™s loop, helps in maintaining a concentration gradient in the medullary interstitium.