Abstract
The shell of Mytilus coruscus consists of two main parts: the fibrous prismatic layer and inner nacreous layer. The former is composed of minute calcite needles and the latter of aragonite platelets. The minute calcite needles are arranged oblique to the shell surface and can be distinguished from the prisms of many other species of pelecypods, owing to their small size and the acicular arrangement. The conchiolin intergrown with inorganic materials in Mytilus coruscus has been studies with an electron-microscope, especially in the ultra-thin sections in order to analyze its ultrastructure. The conchiolin structure in the prismatic layer generally shows the so-called "honeycomb pattern," one chamber being about 2-3μ in horizontal section, as shown in Pl. I, Fig. 1. Furthermore, the conchiolin itself is a very thin curved membrane, less than 100Å in thickness and has no special structure. In addition a few granular matters are recognized inside of each chamber of the honeycomb pattern or attached to the conchiolin membrane in low magnification, as shown in Pl. I, Fig. 1. In high magnification, these granules appear as very minute tubes about 800 A in outer diameter, as shown in Pl. II, Fig. 3 and Pl. III, Fig. 3, and have some periodic patterns in their side walls. Judging from many sections, it seems that these tubes are flexible and free in the top ends, and are connected with the conchiolin membrane in other ends, as represented schematically in Text-Figure 2. The conchiolin in the nacreous layer is very different from the above-mentioned one, and is arranged layer by layer, about 20-25 layers in 10μ span, in the vertical section. In the oblique section, the membrane shows GREGOIRE'S "tight pelecypod pattern." Moreover, they are connected with each other by very fine radial or vertical wall. Namely, the conchiolin intergrown in the nacreous layer consists of the two different membranes as stated above, resulting in the formation of many minute flat or lenticular chambers. The results show that the conchiolin membrane in Mytilus coruscus, especially in the prismatic layer, is entirely different from the one in M. edulis reported by C. GREGOIRE, and has particular structure with minute flexible tubes.
