Functional Morphology of the White Bodies of the Cephalopod Mollusc Sepia officinalis

The white bodies and blood cells of the cuttlefish, Sepia officinalis , were investigated using light microscopy and electron microscopy. Each white body is supplied with arterial blood by two branches of the ophthalmic artery. These two branches arborize into the tissue and form an extensive capillary network that appears to be confluent with a system of thin‐walled venous channels in the white bodies. This vascular arrangement appears to allow maturing cells to leave the white body tissue and enter the general circulation. The putative hemopoietic cells are embedded in an internal connective tissue network. In addition to an extensive extracellular matrix system, this network contains many obliquely striated muscle fibers that probably aid in microcirculation. The white body cells were grouped into four categories that, ultrastructural evidence suggests, represent developmental stages of a single cell line. Morphological similarities between the putative final developmental stage of this cell line and circulating blood cells strongly support the hypothesis that white body cells are hemopoietic in function. Several lines of evidence indicate that proliferation within this cell line occurs at the first two stages of development. Thus a new developmental scheme is proposed. Quantitative analyses have shown that the white bodies are structurally and functionally uncompartmentalized. A comparison of developmental stages suggests that the physiology of the white bodies shifts from proliferation to differentiation as the animals mature. Blood cell densities decrease as the animals mature. Finally, cytological evidence indicates that the white bodies of Sepia officinalis are involved in reticuloendothelial functions in addition to hemopoiesis.