The packing of spheres in embryogenesis and carcinogenesis

Fertilization of the mammalian ova results in the formation of a compact ball of cells, the morula, which then transforms into a hollow sphere of cells, the blastula. The formation of these structures is considered to be dependent on the number and shape of the cells present and approximates to the problem of maximal sphere packing. Similarly, the shape of organs, to some degree, is considered to be dependent upon the shape of the constituent cells which predetermines their maximal packing densities. Implicit in this concept is that like-cells divide until they reach their maximal packing density and are then inhibited from further replication by three dimensional contact inhibition. In this context, tumour cells may be considered as pleomorphic relative to the tissue in which they arise and form a benign tumour, whereas malignant tumours display pleomorphism within the tumour mass.