43.Animals belonging to Phylum chordata possess a notochord: A. During embryonic life only B. Throughout life C. Either throughout or during embryonic life D. None of the above
Option C. Notochord is a rod shaped structure of large vacuolated cells lying between nerve cord and digestive canal along the mid dorsal line of body. Chordates are characterised by presence of notochord at any developmental stage of their life and are classified as non vertebrates and vertebrates. Birds (aves), fishes (pisces) and snake (reptiles) are vertebrates that exhibit replacement of notochord with skull (that encases brain) and vertebral column (that encases spinal cord) during the course of growth and development of animal. This makes options A, B and C incorrect. Amphioxus is a non vertebrate that have notochord throughout the life but lack vertebral column/backbone.
