



Microns 



200 



Figure 83. — Cross section of the radial muscle of the mantle of an adult C. virginica. 



two nerves. Bouin .3, hematoxylin-eosin. 



The muscle completely surrounds 



witli true transverse striation, described in tlie 

 mantle of Pecten jacobaeus and P. opercular)': 

 (Dakin, 1909a), are not found in the oyster mantle. 



BLOOD VESSELS 



The principal blood vessels of the mantle 

 (fig. 232 in ch. XI) are the circumpallial artery 

 (cr.p.a.), which runs along its entire periphery and 

 sends out many branches; tlie common pallial 

 artery (co.p.a.); and a large pulsating vessel in 

 the anteroventral part of the mantle called the 

 accessory heart (fig. 236 in ch. XI). The latter 

 can be observed by dissecting the wall of the 

 epibranchial chamber and spreading the cut tis- 

 sues apart. The structure and function of these 

 vessels are discussed on page 2.53. 



The small arteries and veins of the mantle can 

 be recognized easily bv their histolo2:ical charac- 



teristics. The walls of the arteries have a thick, 

 elastic, muscular layer lined with endothelium 

 (fig. 81, end.). In the veins the elastic layer is 

 much less developed and the endothelium absent 

 (fig. 85). The sinuses (fig. 79) are irregularly 

 shaped spaces in the connective tissue. Since 

 they have no walls of their own tliey cannot con- 

 tract. The size of the opening or lumen may be 

 reduced by growth of the surrounding vesicular 

 cells and by accumulation of Ijlood cells. 



EPITHELIUM, TENTACLES, AND NERVES 



Both sides of the mantle are covered by cylin- 

 drical epitlielial cells set on an elastic basal mem- 

 brane (fig. 77). Large goblet cells which secrete 

 mucus and cells containing eosinophile granules 

 are abundant on both sides of the mantle. The 

 cells of the side facing the pallial cavity are long 



84 



FISH AND WILDLIFE SERVICE 



