102 THE AMERICAN MIDLAND NATURALIST 
specimen of Amblema peruviana. Figure 7 shows a vertical 
section through the furrow, drawn with the Edinger projec- 
tion aparatus. The lamella are seen to fuse at the top of the 
groove rather than being united by interlamellar junctions. 
At the point of fusion of the lamella where the groove is dis- 
continued, the cells are much larger than the usual epithelial 
cells and are closely packed together. The nuclei at, this point 
are spherical (circular in optical section) instead of the or- 
dinary ellipsoid form, probably due to the crowding of the 
cells. These cells are apparently similar in function and 
structure to the large gland cell found between the frontal 
and latero-frontal epithelium on each side of the filament 
(figure 3 g.c.). However these glands cells in the groove 
are not mulatinucleated like the ones on the filaments 
(figure 4 b.), that they have a glandular function is evident 
from their large size (four microns by five microns), their 
lack of cilia, and their granular cytoplasm. This function 
would corresepond with Allen’s discovery that food particles 
imbedded in mucous globules were transported along the 
groove, since it accounts for the source of the mucous. 
The sides of the groove are covered with latero-frontal or 
rather an epithelium corresponding to it. They are slightly 
larger than the latero-frontal cells, being five to seven microns 
long, and three to five microns in width; they both possess 
the characteristic long cilia, which in this case sometimes 
reach a length of as great as twenty microns; the measure- 
ments of the cilia were difficult to record due to the entangling 
with those of other cells. These long cilia undoubtedly serve 
to convey the food and mucous along the groove. 
IV.—SUGGESTIONS AS TO THE CAUSES OF THE 
PHENOMENON AND POSSIBLE SOURCES OF ERROR. 
In the different kinds of epithelium of the gill the clue to 
the selection of food particles and the rejection of mud and 
sand might be found. Allen has shown that foreign substan- 
ced like carborundum, carmine, etc., although introduced 
into the incurrent siphon are never found in the alimentary 
tract (Allen 1). He explains this fact by the action of the 
cilia on the labial palps. The cilia on the gills might help in 
