Figure 64. — Mechanical model of the ligament of C. 

 virginica. Arches are in scale and correspond to the 

 curves visible in a cross section of the ligament at a 

 magnification of about 100 X . Diameter of rubber tub- 

 ing representing fibrillae is not in scale. 



in the formation of the mature 640 A. period 

 collagen (See pp. 512-513 of S. L. Palay [editor] 

 Frontiers in Cytology, 1958), as well as smaller 

 fibrils in the embryonic tissues. The latter 

 probably represent a very early stage in the 

 formation of collagen. 



Collagen fibers can be tanned in vitro, that is, 

 they can be converted by various agents to a form 

 in which they swell less and develop greater 

 chemical resistance. The taiming of protein 

 structures by an orthoquinone occurs naturally 

 among many invertebrates and has been demon- 

 strated for the cuticles of a number of arthrojjods 

 (Dennell, 1947; Pryor, 1940; Pryor, Russell, and 

 Todd, 1946) and for the cliaetac of eartliwornis 

 (Dennell, 1949). There is also evidence that a 

 similar phenomenon takes place in the ligaments 

 of bivalves (Friza, 1932). In Anodorda, for in- 



stance, the amber coloration of the lateral layer of 

 the ligament is considered to be the result of tan- 

 ning by an ortli(K|uinone. This conclusion is 

 based on the fact that even after boiling this layer 

 induces rapid oxidation of the mi.xture of dimethyl- 

 para]ihenylenediamine and a-naphthol (Nadi re- 

 agent), which is frequently employed to indicate 

 the presence of orthoquinones in the cuticles of 

 insects and crustaceans (Dennell, 1947). In the 

 ligament of 0. edulis the differentiation between 

 the two layers may be made visible by Mallory 

 triple stain. The lateral layer (tensilium) consists 

 of quinone tanned protein whereas the central 

 layer (resilium) is built of calcified proteins (True- 

 man, 1951). 



Few chemical studies have been made on the 

 ligaments of oysters, but chemical analysis of the 

 two portions of the ligament of the related 

 pelecypod Tellina made by Trueman (1949) shows 

 the following difTerences summarized in table 10. 



It is rather surprising to find that an elastic, 

 nonliving structure functioning through a con- 

 siderable period of time (according to Trueman, 

 several years in Tellina) is heavily calcified. Tlie 

 resilium of C. virginica contains a mucli larger 

 amount of calcium carbonate than the outer parts: 

 determinations made in my laboratory on the 

 ligaments of 5- and 6-year-old oysters dried at 

 55° C. show that the calcium carbonate content 

 of the resilium varied from 30 to 67 percent of the 

 total weight of the sample, while in the tensilium 

 the content of calcium carbonate was only from 

 5.3 to 8.5 percent. 



It is apparent that f:nowledge of the chemistry 

 of conchiolins and other substances found in 

 molluscan shells and ligaments is incomplete and 

 that much remains to be discovered about the 

 composition and structure of these proteins which 

 play such an important role in tlie life of all 

 bivalves. 



Table 10. — Results of chemical tests of the ligament of 

 Tellina tenuis, according to Trveman 



Five ptTcent HCI 



Saturated KOII (hot) 



Xanthoproteic reaction... 



Millon's reagent 



Ritiret reaction 



Ninitydrin 



Morner's reagent 



("hitosan test (Camphell) 



Chitintest (Schulze) 



Argentaffine 



Outer 

 layer 



Inner 

 layer 



No effect 

 -\11 dissolves 



+ 



-I- 

 + 



Faint . 



58 



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