FEEDING HABITS OF FRESHWATER MUSSELS. 137 



is dissolved when food is lacking, and as it is a proteid, why is not 

 Sedgwick's theory as to its being a reserve food supply also true? 



(2) The presence in the core of the crystalline style of cells 

 similar to those found in the liver epithelium leads Mitra to 

 conclude that the liver is the probable origin of the structure. 

 This also does not seem well substantiated, especially in species 

 where the style is found in a diverticulum. No channel for the 

 passage of a secretion from the liver to the seat of the style has 

 been discovered, and the ciliation of the stomach and intestine 

 forbids their aiding in its transmission. 



Since the publication of the above paper Grave ('03) has sug- 

 gested in his work on the oyster that the crystalline style may 

 perform the duty of preventing coarse particles from passing 

 through the digestive canal. In fresh water mussels I can see 

 but one way in which the style may attend to that function by 

 digesting the said particles. There are at least two objections 

 to this explanation for fresh water mussels (i) As we have seen, 

 the animal is well protected against the entrance of such par- 

 ticles. (2) In case they were admitted to the stomach but kept 

 out of the intestine, they would accumulate in the stomach, for 

 it is not equipped with either a muscular or a ciliary system by 

 which these could be expelled through the mouth. Then too, 

 the mouth is no larger than the intestine and no more capable 

 of receiving them. The largest body I have seen in the alimen- 

 tary tract was a fragment of OsciUatoria (or similar form) 

 measuring 1.5 mm. in length. 



FOOD MATERIALS. 



No one but Zacharias ('07) seems to have undertaken a detailed 

 examination of the contents of the alimentary tract of the fresh- 

 water forms, so I give the results of a purely qualitative examina- 

 tion. In marine mussels it is said that the food consists almost 

 altogether of minute plant forms, and of these almost all are 

 Diatomaceae. In the mussels which I examined I found a some- 

 what different condition. In the first place there is a little 

 higher proportion of animal food present. Living animals are 

 found but rarely, and most of these are apparently living tran- 

 siently upon the contents of the tract. But the mussel does 



