This is a review of the book "Memory Evolutive Systems; Hierarchy, Emergence, Cognition', by A. Ehresmann and J.P. Vanbremeersch. I welcome the use of category theory and the notion of colimit as a way of describing how complex hierarchical systems can be organised, and the notion of categories varying with time to give a notion of an evolving system. In this review I also point out the relation of the notion of colimit to ideas of communication; the necessity of communications to be symbolic representations; and the use of an analogy with mathematics to spell out some of the necessities of such a mode of communication to be powerful, robust and efficient.