What characteristics were used to classify organisms before woese's tree of life analysis?

The unique structure of the neuron is dedicated to the efficient and rapid transmission of neural signals. the relationship between neurons, the spinal cord, and the brain constitutes an elaborate communication system throughout the human body. all but one of the functions listed below are a result of this interaction.

What does the number 18.9984 represent in the image?

What is the meaning of exocytosis ?