Chitin is non living and non-cellular and is secreted by the underlying epidermis. It is a protein-carbohydrate compound. It is composed of several different substances. It is really made up of an outer waxy layer, a middle horny layer and an inner flexible layer. These layers are modified among the various arthropods and also among the different parts of the body. In some, the chitin is soft and permeable (aquatic insects) while in others it forms a veritable coat of armour (terrestrial insects). Between joints and between segments, it is flexible and thin to permit free movements. It is harder in crustaceans where it is infiltrated with calcium salts. In…

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