the epithelium is not attached to the ligament as 

 was described by Moynier de Villepoix (1895). 



At regular intervals the row of epithelial cells 

 is interrupted by oval-shaped pockets which 

 appear to be empty, with the exception of oc- 

 casional amoebocytes and a few connective tissue 

 cells. The significance of these pockets is not 

 clear. The elastic membrane under the epi- 

 thelium, thicker here than in the other parts of 

 the mantle, includes many muscle fibers arranged 

 parallel to the length of the ridge (m.). Large 

 oval cells containing yellow-brownish granules 

 (pig. c.) are abundant. The ridge is well supplied 

 with blood through a large blood vessel (bl. v.), 

 around which the connective tissue consists of 

 tightly packed globular and spindle-shaped cells. 

 Directly under the basal membrane of the ridge, 

 however, the connective tissue of the mantle is 

 made up of large vesicular cells. 



FUNCTIONS OF THE MANTLE 



Ciliary currents along the inner surfaces of the 

 mantle form a definite pattern which may be 

 easily observed. If one valve of the oyster is 

 removed the corresponding mantle rolls up and 

 exposes the gills and the inner surface of the man- 

 tle on the opposite side. In such a preparation 

 the intact lobe of the mantle remains fully 

 stretched and the ciliary currents can be observed 

 by sprinkling the surface with small quantities of 

 carmine, colloidal carbon, powdered shell material, 

 carborundum, or other powders insoluble in sea 

 water. It is best to use very fine particles, such 

 as powdered mineral wiUemite and colloidal 

 carbon. Willemite phosphoresces a brilliant green 

 under ultraviolet light, which makes it possible 

 to locate even the tiniest particles not otherwise 

 recognizable. As a source of ultraviolet light I 

 used a small Mineralight lamp. Hard and heavy 

 particles of this mineral may stimulate the cilia 

 by their weight, but this difficulty is avoided by 

 using colloidal carbon. 



As can be seen from the diagram in figure 90, 

 drawn from life, the general direction of the cur- 

 rents is from the base of the mantle to its periph- 

 ery, with the ciliary motion strongest in the 

 anterodorsal sector. In the large oyster (5 inches 

 in height) used for the drawing, this area extended 

 along the margin of the mantle from the level of 

 the labial palps approximately halfway down the 

 anterior side. The upper part of the mantle was 

 usually completely cleared 2 or 3 minutes after 



Centimeters 



Figure 90. — Discharge areas of the mantle. Note the 

 two large lumps of the discarded material at the edge of 

 the mantle which mark the boundaries of the principal 

 discharge area. Small arrows indicate the direction of 

 ciliary currents. The clear path along the periphery of 

 the mantle in the upper left side, indicated by short 

 arrows, marks the ciliary tract located over the circum- 

 pallial artery. Long arrow at right indicates the direc- 

 tion of exhalant current of the cloaca. Drawn from life. 



it was sprinkled with powder, while in the same 

 specimen 5 to 10 minutes were required to clear 

 the lower (ventral) part. Although the ciliary 

 currents along the posterior side of the mantle 

 in the area adjacent to the cloaca are also directed 

 from the base toward the periphery, this area is 

 swept clear by an exhalant current from the gills 

 (fig. 90, long arrow) which is much stronger than 

 those produced by the mantle epithelium. 



The currents along the anterodorsal part of the 

 mantle (upper left of the figure) adjacent to the 

 lal)ial palps are directed at an acute angle to its 

 free margin. There is also a well-defined tract of 

 ciliary movement about 1.5 mm. wide parallel to 

 the edge of the mantle. Upon reaching the level 

 of the lower corners of the labial palps this current 



90 



FISH AND WILDLIFE SERVICE 



