0.3 



Millimeter 



Figure 89. — Localization of alkaline phosphatase in the mantle of C. virginica (longitudinal section). 



of a preparation treated by Gomori method. 



Photomicrograph 



vations are in full agreement with the results 

 obtained by Bevelander (1952). 



SUBLIGAMENTAL RIDGE 



A small ridge marking the dorsal edge of the 

 mantle along the fusion of its two lobes is known 

 as the subligamental ridge. Its length in the 

 anteroposterior du-ection corresponds exactly to 

 that of the ligament, which is secreted by the 

 epithelial cells of the ridge. The base of the 

 ridge is flattened and rests on basic elastic mem- 

 brane; the body of the ridge is semicjiindrical in 

 cross section, its surface slightly undulating, as 

 can be seen from the longitudinal section sh(')wn 

 in figure 7S. 



The histological structure of the ridge has been 

 studied in MijMlu.y (List, 1902; Tullberg, ls,si), 

 in Anodonta (Moynier de Villepoi.x, 1S95; 

 Rassbach, 1912), and in the Portuguese oyster 

 Crassostrea (Gryphaea) angulata (Leenhardt,I926). 

 Leenhardt and Moynier de Villepoix call the 



structure "bandelette paleale" (pallial strip) but 

 the term subligamental ridge seems to be more 

 descriptive. 



In C. virginica the subligamental ridge is always 

 well developed and easily recognizable by its 

 shape and by its coloration, which is usually 

 darker than that of the adjacent part of the man- 

 tle. The epithelium (fig. 7S, ep.) covering the 

 ridge presents a most striking picture. It con- 

 sists of a layer of extremely tall and narrow cells 

 arranged in fanlike groups and set on a well- 

 developed basal elastic membrane. The length 

 of the cells varies from 50 to 200 n depending on 

 the position they occupy within the layer. The 

 cells are very thin, with granular protoplasm and 

 an oval-shaped nucleus. At the distal portion 

 of the ridge the boundaries of the cells become 

 indistinct and their protoplasm darker, presum- 

 ably due to the concentration there of the organic 

 material which thej' secrete. The free surface of 



THE MANTLE 



89 



