Anatomy and Physiology of Anodonta Fluviatilis. 177 



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 c.ause 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 jabial 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, aerating 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 oesophagus into the stomach, and from the stomach 

 through the intestinal canal, passing out of the anus ; the nutritive 

 portion having been digested and assimilated. 



Mouth, Stomach, Alimentary Canal. 



(Plates 6, 10, 11, 13.) 



The mouth or oral aperture consists of a broadly oval, nearly circu- 

 lar, horizontal aperture (PI. 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 



