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.
The nervous system consists of two main parts: the central nervous system and the peripheral nervous system: The central nervous system is made up of the brain and spinal cord. The peripheral nervous system is made up of the nerve fibers that branch off from the spinal cord and extend to all parts of the body, including the neck and arms, torso, legs, skeletal muscles and internal organs.