Studies on the coelomic cells and haemal system of some echinoids

Abstract

The investigation was based on a study of the fine structure, locomotion and function of the perivisceral coelomic cells of Diadema antillarum (Philippi) and Psammechinus miliaris (Gmelin). The flagellated cells are probably not parasitic and may be unique amongst metazoan cells. The phagocytic bladder amoebocytes effect coagulation, first becoming filiform, then elongating to entangle cells in a clot. Inhibition of coagulation must be cautiously interpreted. Vapour fixation and a new method of identifying fixed, stained cells were utilised with histochemical tests to investigate the composition of the inclusions of the spherule amoebocytes. It was concluded that the red spherules are not associated with appreciable amounts of protein or lipid, contrary to previous opinion. These spherules are however associated with carbohydrate, probably a sulphated mucopolysaccharide. The often-quoted statement that the colourless spherules are 'albuminous' is now substantiated. Adam's (1957) test for indoles and chromatography of extraxts indicated that tryptophan might be an important constituent. There is an apparent correlation between reduction of the indole content of the colourlessspherules of Psammechinus miliaris and the onset of gonad maturation. It was concluded from a re-examination of Stott's, (1955),work that absorption from the stomach lumen by amoebocytes has not been demonstrated, and probably does not occur. The haemal system has been investigated. Existing accounts, in both original and text-book versions, are significantly different from what was observed in Echinus esculentus (Linnaeus) and Psammechinus miliaris, (Gmelin), In these species the radial strands could not be detected and the aboral haemal area was ill-defined. However, contrary to recent statements, there are contractile haemal vessels round the stomach, and there is considerable fluid movement within these vessels, which may comprise a circulatory system. Preliminary experiments indicate that these vessels may be concerned in the initial absorption of material from the stomach lumen.