In the previous chapter I argued that in the context of GA I Aristotle uses the hylomorphic model primarily as a way to analyse the causal contributions of male and female seed to the formation of the primitive embryo (embryogenesis). In this context semen is said to give form to the menstrual blood only in the purely mechanical sense of imposing a determinate limit or boundary on her indeterminate fluid. In GA II 4–5 Aristotle uses the hylomorphic analysis as a way to identify the parents’ reproductive contributions to the substance that comes to be from the embryo (the completed offspring). He presents his account in two stages. In GA II 4 he argues that the father provides the offspring’s form in the sense of its soul while the mother provides the body that underlies the soul as its subject. He then refines this account in GA II 5 by identifying the father’s exclusive contribution with sensory soul.