We learn that the equator is a line around the wide waist of the world. Pleasure cruisers often make a great toâdo about crossing this line on the ocean. Any passenger who owns up to the fact that this is his first crossing may be put through ceremonies such as walking the plank and other merry goingsâon.
Ectoderm â Outer or External Layer â differentiates into the nervous system, epidermis, and the outer part of the integument system â forms the central nervous system, the lens of the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands.
Central Nervous System. In vertebrates, the central nervous system consists of brain, and the spinal cord. Brain: - It is the most important organ which is lodged in the brain box, called cranium. Brain is covered by membranes called meninges.