58 MUSSEL FAUNA OF MAUMEE RIVER. 



and placed in the calm shallow waters of a lake. It is probable that 

 these mussels breathe extra heavily in the less highly oxygenated 

 lake water. The current from the exhalent siphons boils up vio- 

 lently and is ejected intermittently at more or less regular intervals. 



In many mussels there is no direct communication between the 

 gill chamber into Avhich the water, bearing solid particles, enters, 

 and the suprabranchial chamber from which it is ejected through 

 the exhalent aperture. Some mussels have the gills free above pos- 

 teriorly, so that the two chambers have direct communication, and 

 in these it is possible for the mussels to shunt solid particles directly 

 from the gill chamber to the chamber above without passing through 

 the alimentary canal. We have no evidence, how^ever, that this is 

 ever done. The mussel probably exercises little choice as to the 

 nature of its food. The papillae which fringe the edge of the in- 

 halent orifice are supposed to be water-testing organs, and the mussel 

 can close itself against foul water or against positively objectionable 

 material. In the feeding mussel, as observed in the stream or lake, 

 there is no appearance of nicety or fastidiousness as to the particles 

 swept in ; the wide open, immobile, and expressionless lips admit the 

 general current and its diverse minute population with a catholic 

 impartiality. The alimentary canal of the mussel is usually filled 

 with a sort of impal^Dable or sometimes gritty mud, and mixed in 

 with this are found scattered organisms of various sorts which serve 

 as food. 



The impalpable mud usually corresponds closely in color and 

 general appearance with the bottom in which the mussels are found ; 

 in rivers with yellow clay bottoms it is yellowish; in dark, muddy 

 bottoms it is dark. It consists of fine particles which have been 

 held in suspension in the water. In turbid streams it consists of 

 the material which gives the water its turbidity, in clear ponds 

 with bottoms of fine mucky silt it is black, and in those still w^aters 

 full of diffused minute algse and flagellates, which are common in 

 ponds and pools, it is predominantly organic and of a greenish cast. 

 In the latter case it usually consists almost entirely of colonies of 

 plankton-scum (water bloom) algae, which are frequently inclosed in 

 clear vacuolelike spaces. 



The moderately long alimentary canal suggests that the ingested 

 material contains a low amount of nutriment; observations also seem 

 to indicate that the digestive powers of the mussel are slow and feeble. 

 In mussels which had been kept for several days Scenedesinus was 

 found as fresh and green as ever, and in one mussel obtained in the 

 reservoir of the feeder canal green flagellates were still alive and ac- 

 tive after having been at least 36 hours in the mussel. ^Vhile in these 

 instances it is possible that digestion was delayed by the capture of 

 the mussel and placing in changed surroundings, there are other indi- 



