A spot is a graph any replica of which occupies a simple bounded portion of a surface, which portion has qualities distinguishing it from the replica of any other spot; and upon the boundary of the surface occupied by the spot are certain points, called the hooks of the spot, to each of which, if permitted, one extremity of one line of identity can be attached.
The expression of a rheme in the system of existential graphs, as simple, that is without any expression, according to these conventions, of the analysis of its signification, and such as to occupy a superficial portion of the sheet or of any area shall be termed a spot. The word “spot” is to be used in the sense of a replica; and when it is desired to speak of the symbol of which it is the replica, this shall be termed a spot-graph. On the periphery of every spot, a certain place shall be appropriated to each blank of the rheme; and such a place shall be called a hook of the spot.
A rhema which is made a part of a graph and is not itself compounded according to the rules of existential graphs is called a spot and the places where proper names might be inserted are called the hooks of the spot.