ANATOMY AND PHYSIOLOGY oF ANODONTA FLUVIATILIS. 17% 
gills of an Anodonta, about thirty hours after they had been removed 
from the animal, in the meanwhile remaining in water, the movement 
of the cilia was apparent, as regular and rapid as during the life of 
the animal ; how much longer the movement’ may have continued I 
do not know. 
The cause of the rapid, rhythmical motion of the cilia has not been 
satisfactorily explained. ‘This movement continues after the apparent 
death of the animal. The integrity of the cells to which they are 
attached is necessary to the movement, for as soon as these shrink 
from want of moisture, or are destroyed from any cause, the movement 
of the cilia ceases. 
The cilia occur on the inner side of the mantle, on the labial palpi, 
the foot, tentacles of the siphon, the margins of the plates of the 
outer side of the gills, in the mouth, stomach and alimentary canal, 
and on the tentacles of the siphon. If a few grains of any colored mat- 
ter, for instance, carmine, is placed in the water near the posterior 
portion of an Anodonta, as it lies in the water in its natural position 
with the shell slightly expanded, it will be observed to enter the bran- 
chial cavity, and in a short time afterward to pass out at the exhalent 
siphon. The cause of this is the action of the cilia. The movement 
of the cilia on the interior of the mantle is toward the anterior end, 
and the water entering the branchial siphon is consequently forced in 
that direction. The movement of the cilia on the margins of the 
plates of the gills is from the ventral to the dorsal portion, and by 
them a portion of the water being forced toward the anterior end, is 
diverted from its course and passes over the gills from their ventral to 
their dorsal :margins, aérating the blood in the capillaries. From the 
dorsal portion of the gills to the posterior portion, the movement of 
the cilia is toward the posterior end; in this manner the water which 
has passed over the gills is forced out through the dorsal siphon. 
The portion passing to the anterior part of the animal is conveyed, 
by the action of the cilia of the palpi to the mouth, by the cilia of 
the mouth and cesophagus into the stomach, and from the stomach 
through the intestinal canal, passing out of the anus; the nutritive 
portion having been digested and assimilated. 
Moura, SromacH, ALIMENTARY CANAL. 
(Plates 6, 10, 11, 13.) 
The mouth or oral aperture consists of a broadly oval, nearly circu- 
lar, horizontal aperture (Pl. 6, m., Pl. 13, figs. 4, 5, m.), situated in the 
anterior portion of the body, just beneath the adductor muscle. The 
mouth is simply an opening or cavity, without any trace of a mastica- 
[Sen. Doc. No. 38.] 23 
