MUSSEL, FAUNA OF MAUMEE RIVER. 59 



cations that digestion is normally slow and imperfect. In mussels 

 taken from the beds, washed, and immediately examined, diatoms 

 found at the posterior end of the alimentary canal are frequently 

 alive and exceedingly active ; they appear to be even more active than 

 when taken from open water, and the form and color of the chromato- 

 phores are unchanged. It is possible that in these cases the mussel 

 obtains some nutriment from the outer coating of the diatom and that 

 the removal of this makes the latter especially active. 



The organisms found in the alimentary canal of mussels vary con- 

 siderably with the places in which the mussels live, but, so far as 

 observed, do not differ much, if at all, among the various species. 

 They consist of such planktonts as are small enough to be taken in, 

 and not active enough to resist the force of the inward current pro- 

 duced by the mussel. The largest and most active planktont taken 

 to any extent was the entomostracan Bosminia. This was found 

 with considerable frequency in lake-dwelling mussels, but as all seen 

 were dead, and many were simply empty shells, it was not possible 

 to ascertain whether the mussel had taken in the living animals or 

 not. Actively moving flagellates are quite frequently ingested. In 

 the gill chamber of some Quadrula tuberculata^ a species with an 

 exceptionally large inhalent opening, we found such objects as Chiro- 

 nomvfi larvae and one small mature dipterous insect. 



There are several organisms which are likely to be found in mus- 

 sels wherever taken. Species of Scenedesmus are almost invariably 

 present, as is also Navicula along with other diatoms and species of 

 Pediastrum^ such as P. pertusum with great frequency, P. horyaivuin 

 rather commonly, and P. ehrenhergii, which appears to be a rare 

 species everywhere, only occasionally. The rotifer Anurcea cochlearis 

 is also found frequently and under all sorts of conditions, in lakes, 

 ponds, and rivers. The part usually found is the empty lorica. 

 Another common object found in the alimentary tract of mussels is a 

 club-shaped, several -celled, brown object, probably the spore of a 

 fungus or lichen. 



With the exception of those just mentioned the organisms found 

 within mussels are very diverse, and the creatures seem to be quite 

 omnivorous within the limits of what they can capture. Just as in 

 any stream one finds various types of plankton aggi'egates from the 

 extreme type of " potamoplankton " or characteristic river plankton 

 of the mid-current, recognizable by the scarcity of water-bloom algse, 

 to well-developed types of " limnoplankton " or lake plankton in the 

 quiet sloughs and bayous, so in these different portions of the stream 

 one finds different sets of organisms in the mussels. In lakes full of 

 diffused water-bloom algse, the material which forms the mudlike 

 matrix of the food in river mussels is to some extent replaced by the 



» Not in the Maumee River, however, where few were examined. 



