The structure of the scales of Latimeria chalumnae



Scales from four specimens of Latimeria chalumnae were examined in a dissecting microscope and then X-rayed. Some were demineralized and prepared for routine histology. Others were cleared in cedarwood oil. Ground sections of plastic embedded scales were micro-radiographed and electronmicrographs made of araldite embedded frozen scales. Corresponding 1 μm thick serial sections were examined in the light microscope.

The greater part of the scale is composed of layers of unmineralized isopedine surmounted by the exposed portion of the scale which is pigmented and ornamented by a series of denticles of tubular dentine tipped with enameloid. Between these two parts is a thin ridged bone-like layer. In the electron micrographs the isopedine was seen to consist of layers of densely packed collagen fibres; the orientation of which was uniform in each layer but varied markedly from layer to layer. Only few cells were found between the fibre bundles.

The X-rays revealed numerous concentric annulae and, lying approximately at right angles to these, a further series of ridges radiating from the centre of the scales.

It is suggested that the basal unmineralized isopedine and the ridged layer of bone-like tissue covering it represents a highly modified cosmoid scale on which the denticles and pigmented layer have become superimposed.