The spinal cord begins at the occipital bone and extends down to the space between the first and second lumbar vertebrae; it does not extend the entire length of the vertebral column.
Earthworms are invertebrates, lacking a skeleton. To support and shape the body, they are filled with coelomic fluid. Earthworms sometimes appear to have a belt or saddle around their bodies; this is a clitelum, a structure containing maturing eggs.
There are eight systems in the human body. Each system relies on the other to keep the body functioning. The systems of the body includes the circulatory, immune, skeletal, excretory, muscular, endocrine, digestive, nervous and respiratory. It is important to understand how human body systems work together.