Which brain is composed only of nerve tissue?

The spinal cord and brain are made up of nerve tissue. But besides the nervous tissue, there are other types of tissues in their structure. First of all – connecting. Also, the entire brain is covered with blood vessels and capillaries. Cerebrospinal fluid is located between the membranes and the surface of the brain and spinal cord. It is called liquor. So we see that the brain of any animal cannot consist only of nervous tissue, since it also needs blood supply and protection. And only from nerve cells can small clusters or nodules of worms consist.