CRYSTALLINE STYLE OF LAMELLIBRANCHS 75 



lightly. The nucleus is very large, is situated proximally and 

 may contain one or two nucleoli. Vacuoles or granules of ab- 

 sorbed food material often occur in the cytoplasm. From the 

 distal end of each cell project a number of large cilia, the basal 

 fibers of which extend down some distance into the cytoplasm. 



Beneath the basal membrane are bands of musculature in the 

 carnivorous Septibranchs, but in the other lamellibranchs, as 

 pointed out by Gutheil ('11), ciliary action has entirely re- 

 placed peristalsis, hence muscular elements in this region are 

 lacking. 



Lying between the ciliated cells are two other types, namely, 

 secreting cells and mucous glands. The secretory cells are of 

 long goblet-cell type, and when filled with secretion are greatly 

 distended. They occur most numerously in the minor typhlosole. 



The mucous glands are large unicellular structures which take 

 a deep red color with mucicarmine, and are sharply differenti- 

 ated from all surrounding cells. The nucleus lies near the base, 

 and when the upper portion of the cell becomes filled with 

 mucus it is so distended as to appear ovoid or nearly spherical 

 in shape (fig. 13). These glands in Lampsilis are confined to the 

 minor typhlosole and the intestine. I have never found them 

 in this species in the major typhlosole or the style sac (fig. 2). 



Where the minor typhlosole joins the style sac there is a strik- 

 ing modification of the epithelium. The surface of the cells 

 dips down to form a furrow which extends parallel to the typhlo- 

 sole. The cells bordering this groove are twice as long as the 

 other cells of the alimentary canal, are very narrow, and have 

 large, densely staining nuclei. Their distal ends bear few and 

 small cilia (fig. 13). In favorable material great numbers of 

 globules of a substance staining like the style are found in and 

 between the cells. In figure 14 many of these globules are 

 shown beneath the epithelium. At the surface some of these 

 drops have coalesced to form a mass which cements the style to 

 the epithelium at this point. 



The epithelium of the rest of the style sac differs markedly 

 from that of the above region in that it is composed of shorter 

 and thicker cells. The nuclei are large, rich in chromatin, and 



