Fir.uRE 63. — Electron micrograph of the ligament made near one of the arches parallel to the fibrils of C. virginica. 

 bodies probably correspond to the smallest globules seen in the light microscope. 



Dark 



of the conchiolin of the prismatic hiyer and that 

 of the calcite-ostracum discussed on p. 42. True- 

 man (1949) conchides that the two types of 

 conchiohn seem to correspond respectively to the 

 two components of the hgament. The tensihum 

 gives a positive reaction with the xanthoproteic, 

 Millon's, and Merker's reagents, whereas the 

 reaction of the resihum to these reagents is 

 negative. Brown (1949) points out that most 



of the epithehal skeletal proteins of invertebrates 

 that have been examined seem to be coUagens 

 and that their physical properties depend upon 

 degree of hydration. The electron micrographs 

 of the ligament (figs. 61 and 63) do not, however, 

 show the axial periodicity of about 640 angstrom 

 (A.) which is the most common characteristic of 

 collagen fibrils (Gross, 1956). Other authors 

 describe fibrils of 270 A. period which participate 



THE LIGAMENT 



57 



