Thesis submitted for the degree of Doctor of Philosophy in the University of the Witwatersrand, Johannesburg. / Biology, having outgrown its purely descriptive phase, has, for nearly a century, been in an era of causal analysis. It has been a period of extreme compartmentalisation of the general field into many disciplines, each endowed with a defined range of problems, with peculiar materials of study and with special approaches and techniques.From the nature of things, it is inevitable that each biologist should have been a specialist. The field of living things ramified so vastly that the species of scientist known as the biologist or naturalist became largely extinct: instead, there were geneticists, systematists, physiologists, embryologists, biochemists, cytologlsts and others. Specialisation did not stop even at that point for the systematists split into mammalogists, ornithologists, helminthologists, etc.; the geneticists into experimental geneticists, cytogeneticists, phenogenetlclsts, and so on. Good and bad consequences flowed from this tendency. The advantage of specialisation was a great increase in the store of factual information; the disadvantage lay in the isolation between representatives of the various disciplines and in the absence of cross-pollination in the development and evaluation of concepts. / WHSLYP2017