Figure 77. — Transverse section of the edge of the mantle of adult ('. virginica. Bouin 3, heniatoxylin-eosin. The outer 

 or shell lobe at left faces the valve (not shown) and is bent as a result of fixation. The section passes between the 

 tentacles of the inner lobe (pallial curtain) ; only the tentacle of the middle lobe (m.l.) is seen. c.gl. — conchiolin (or 

 periostracal) gland; conch. — sheet of conchiolin spread over the shell lobe; cp.a. — circumpallial artery; cp.n. — circum- 

 pallial nerve; el.f. — elastic fibers; ep. — epithelium; l.m. — longitudinal muscles of tentacles; m.l. — middle lobe; ob.m. — 

 oblique muscles; p.c. — pallial curtain (inner lobe); per. gr. — periostracal groove; sh.l. — shell or outer lobe; tr.m. — 

 transverse muscles. 



growing season, viscous yellowish material (fig. 

 77, conch.) accumulates in the groove and grad- 

 ually oozes out to the periphery of the outer 

 mantle lobe, where it solidifies into the perio- 

 stracum. The groove between the middle lobe 

 (m.l.) and the pallial curtain secretes mucus, 

 which is gradually moved by ciliary currents to 

 the outer margin of the mantle and there discarded. 

 It has already been noted that the edges of the 

 middle and the inner lobe each bear a row of 

 highly e.xtensible, tapering tentacles; however, 

 their arrangement and size in th-e two lobes are 

 different. Two types are clearly visible along the 

 edge of the middle lobe: numerous short and slen- 

 der tentacles, and less abundant long and stout 



ones (fig. 76). The order of the tentacles follows 

 a certain pattern, namely, each long tentacle is 

 succeeded by a group of four to si.x small ones (t2). 

 The stout tentacles frequently occupy a position 

 slightly out of line with the small ones, being a 

 little nearer to the inner fold. The inner lobe 

 bears only the long and stout tentacles (ti). 



There is great variation in the size of all the 

 tentacles and in their pigmentation. Since they 

 are highly sensitive to touch and other stimidi and 

 retract at the slightest disturbance, tlieir relative 

 size can be observed only wlien they are completely 

 relaxed. In fully narcotized adult oysters the 

 ratio between the niunbers of tentacles on the 



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