Skeletal System.
vertebrae make up the spine (backbone) of vertebrate animals.
The spinal cord itself is part of the nervous system. However, it runs through the centre of the spine, which is part of the skeletal system.
I think the main organs are the brain and the actual nerves.
Lemurs, being animals who have developed notocords, that is, spine, belong to Phyllum Chordata.
The spine is composed of the vertebrae. This is part of the skeletal system. The spinal cord is part of the nervous system.
They belong to the nervous system
The spine is part of the skeletal system. While it contains a very Significant portion of The Nervous System [the spinal cord], the Spine is of osteo-origin; meaning that it is made of [or from] bone-tissue.
The kidneys belong to the excretory system.
Roundworms (scientific name: Nematoda) are invertebrates, as they do not have a spine.
Veins belong to the circulatory system, because they transport blood there for they belong to the circulatory system.
The Spine
The eyes belong to the Nervous system.