The pattern of organization is used by the writers to organize their ideas to effectively communicate the message.
The pattern of organization used can vary depending on the purpose of writing a statement.
The organizational pattern that is used in the sentence "The three parts of an insect's body are the head, the thorax, and the abdomen" is a spatial pattern.
Spatial organizational pattern organizes the information given in a sentence based on the physical relation of objects with each other. This pattern of organization is widely used by the writers to strike up an image of how the various parts are physically located.
Since in the given sentence the head, thorax, and abdomen are located one after the other in a cockroach's body, the pattern of organization used is spatial.
