0.5 



Microns 



Figure 62. — Electron micrograph of a .section of the ligament of C. virginica made acro.ss the fibrils. 



the structure of the ligsiment of C. inrginica has 

 some similarity to that of the organic membranes 

 of the aragonite shells. Recently Stenzel (1962) 

 has found that the resilium of the Ostreidae con- 

 tains aragonite. 



One of the sections of the ligament of C. viryinica 

 studied with the electron microscope shows a series 

 of bhick, oval-shaped bodies arranged along curved 

 lines and separated from one another by fibrils 

 (fig. 63). The black bodies probably correspond 

 to the small globules visible under the liglit micro- 

 scope. Their nature has not been determined. 



The action of the ligament can be demonstrated 

 by a rather crude model consisting of two slightly 

 curved pieces of wood, representing the valves, 

 joined by a series of brass rods. The rods are 

 bent and arranged to correspond to the course of 

 the arches as the latter are seen in an enlarged 

 photograph of a transverse section of the ligament 

 (fig. 57). Thin rubber tubing interwoven between 

 the arches corresponds to the bundles of fibrils. 

 Since the diameter of rubber tubing used in the 

 construction of the model greatly exceeds the 

 comparable diameter of the fibrils, this portion of 

 the model is not in scale. Another departure 



from actual conditions is the interweaving of the 

 rubber tubing between the arches, a method used 

 to simplify construction although no such arrange- 

 ment of fibrils was disclosed by microscopy. The 

 model is shown in fig. 64. If the sides of the 

 structure are pressed together, the arches curve 

 up and exert lateral pressure at the same time 

 that the increased rigidity of the rubber tubing 

 adds to the elastic force. One can easily feel this 

 pressure by touching the rubber tubing witli the 

 finger tips while bringing the "valves" together. 



CHEMICAL COMPOSITION 



The chemical composition of the ligament is 

 essentially the same as that of the organic matrix 

 of the shell (Mitchell, 1935: Trueman, 1949, 

 1951). The proteins forming the lateral (tensil- 

 ium) and the central (resilium) portions of the 

 ligament are not, however, identical. The differ- 

 ence can be demonstrated by staining reactions 

 and by various chemical tests. For instance, in 

 Tellina tenuis the lateral parts of the ligament are 

 stained red or yellow by Mallory triple stain, 

 while the inner part turns blue, a difl'erence 

 comparable to that between the staining reaction 



56 



FISH AND WILDLIFE SERVICE 



