Kessel, Joan2015-05-132015-05-132015-05-13http://hdl.handle.net/10539/17736The present study investigates the cellular events involved In the organization of a mass of mesenchymal cells into a three-dimensional pattern of blood vessels, blood cells, and coelomic linings. This study has been carried out in both the AP and AOV, affording an integrated understanding of this morphogenesis throughout the blastoderm. Attention has been focused on the dorso-ventral and proximo-distal polarities in the developmental properties of the components of this system, and the roles of the associated germinal layers (the ectoderm and endoderm) in these two regions in the temp orally and spatially appropriate creation of this pattern.enThesis