Accurately determining and classifying the structure of complex networks is the focus of much current research. One class of network of particular interest are metabolic pathways, which have previously been studied from a graph theoretical viewpoint in a number of ways. Metabolic networks describe the chemical reactions within cells and are thus of prime importance from a biological perspective. Here we analyse metabolic networks from a section of microorganisms, using a range of metrics and attempt to address anomalies between the observed metrics and current descriptions of the graphical structure. We propose that the growth of the network may in some way be regulated by network size and attempt to reproduce networks with similar metrics to the metabolic pathways using a generative approach. We provide some hypotheses as to why biological networks may evolve according to these model criteria.