Fill in the Blank Questions 35.In flatworms, protonephridia branch throughout the body into bulblike _______________. 36.The regulation of the body’s osmotic composition is called __________________. 37.The process of removing and ridding the body of toxic nitrogenous wastes from the blood is called ______________. 38.The _____________ is the functional unit within the kidney. 39.________________ is the final product to be expelled from the body after the kidney has reabsorbed needed nutrients and water. Â Â