Antidiuretic hormone (ADH) controls the tubular permeability and concentration of sodium in the extracellular fluid. It regulates the osmotic pressure of body fluids by causing the kidneys to increase water reabsorption.

It associates with the renal pressure system and then regulates the fluid volume of body through the agency of hypothalamic osmoreceptors.

Silk fibre is formed of two proteins namely fibroin and sericin.

Diencephalon is located between cerebral hemispheres above and midbrain below. Its cavity is known as the third ventricle or diocoel. It is connected to each lateral ventricle of cerebral hemisphere by foramen of Monro, seperately.

Prothoracic gland is also known as moult gland in some arthropods and Y organ or ventral gland in crustaceans. It secretes moulting hormone called ecdysone or ecdysome, which is steroid and stimulates moulting or ecdysis during metamorphosis in insects.

Vitamin- C (ascorbic acid) has virucidal property. It is water soluble vitamin, ie, it dissolves in water and its excess amount is excreted in urine.

In radial symmetry, body is divided into two similar halves by more than two planes passing through the main axis.

Cnidarians or coelenterates such as Hydra, sea anemone, Aurelia, Obelia etc are radially symmetrical animals with cell- tissue grade of body organizations.

Sol- gel theory of amoeboid movement was first given by Hyman, later supported by Pantin (1923) and Mast (1926). According to this theory, amoeboid locomotion is due to change in the viscosity of cytoplasm.

The middle ear cavity in mammals characteristically contains a chain of three little bones or ear ossicles extending between the tympanic membrane and the fenestra ovalis. These are called malleus (hammer), incus (anvil) and stapes (stirrup) because of their characteristic shapes.

In the structure of compound squamous epithelium, several layers of cells, deep layers are cuboidal to columnar, surface layers flat and scale- like. 

It is found in mouth, oesophagus, part of epiglottis (pharynx) and vagina. The main function of this epithelium is protection.

Solenocytes or flame cells are the excretory organs of Phylum- Platyhelminthes.