

■'V■\\^lWli^^;'^■^■i^>:^|l;v;i 



'^0i0iM^^ih. 



'." ***' ' ""' * '"' y '^ '.. -■;"■■■■■■■■' --"v •■■■-- ^^ ■' — 



"...  ' ■: ; . ^,^-.■■M V,  



;.•■■ 









Millimeters 



0.5 



Figure 57. — Cros.s .section of the central portion of the ligament of C. virginica made perpendicular to the pivotal axis 

 of the valve. Arches (curved lines of dense material) extend from left to right: the valves are not shown in the 

 drawing. 



fibrillar, but at higher magnification the fibrillar 

 structure becomes clearly visible. Two types of 

 fibrils can be distinguished on the photomicro- 

 graph of tensilium shown in figure 60. Heavy and 

 well-defined bundles of fibers originated along the 

 vertical jdane of the lamellae (up and down bundles 

 in fig. 60) and short and slender fibrils in places 

 at right angles to the large bundles (the lower 

 half of fig. 60). Large oval-shaped bodies on 

 the upper right and lower left part of the figure 



are the accumulation of calcium carbonate crys- 

 tals. Single minute crystals are scattered over 

 the body of the lamella. The outer dark layer 

 is very thin, its color is due to densely packed 

 narrow iilirils. Large and small globules which are 

 conspicuous in tlie architecture of the resilium 

 are absent in the tensilium, and the structure of 

 the latter lacks the complex arrangement of 

 globules and fibrils found in the former. 



Tlie complexity of the microscopic structure 



THE LIGAMENT 



51 



