Lake Maxinkuckee, Physical and Biological Survey 47 



the lake mussels are almost always full enough of alg^e to be more 

 or less flecked with green and sometimes the whole mass is de- 

 cidedly greenish. On being placed in a vial of preserving fluid 

 (3% formalin was generally used) and shaken, the material from 

 the river mussels always retains the uniform appearance of mud ; 

 that from the lake mussels separates, the mud settling to the bot- 

 tom and the organic material settling as a light flocculent mass 

 above the more solid portion. This top layer is composed of the 

 various plankton elements of the lake, and was found to vary con- 

 siderably in different lakes. In the Lake Maxinkuckee mussels it 

 was found to consist chiefly of such species as Microcystis aerugi- 

 nosa, Botryococcus hraunii, Coelosphaeriuni kuetzingianum, various 

 diatoms, such as species of Navicula, Rhoicosphenia, Gomphoneyna, 

 Cyclotella, and Cocconema, various forms of desmids, especially 

 Cosmarium and Staurastrum, various forms of Scenedesmus, con- 

 siderable Peridinium tablulatum, and short filaments of Lyngbya. 

 Ped.iastrum, both horyanum and duplex are here, as almost every- 

 where, rather common objects encountered in the intestines of 

 mussels. Casts of the rotifier Amiraea cochlearis, and of the small 

 entomostracan Chydorus, were occasionally encountered. In one of 

 the Lost Lake mussels, Dinobryon, an exceedingly frequent ele- 

 ment of the mussel-food in Lake Amelia, Minn., but rare here, was 

 found. 



No opportunities were had to study the stomach contents during 

 the winter, the mussel work having not been taken up to any great 

 extent during the earlier part of the survey. Mussels obtained 

 quite late in the autumn contained much the same material as in 

 summer. The open and apparently active inhalent and exhalent 

 apertures noted throughout the winter in some individuals would 

 indicate that the mussels — at least some of them — do not hiber- 

 nate, but carry on life processes more or less actively the year 

 round. The presence of pretty well marked growth-rings would 

 indicate, however, annual rest periods. As diatoms appear to be 

 much more abundant in the water during the winter, it is probable 

 that they enter more plentifully into the mussel's bill-of-fare dur- 

 ing the late autumn, winter and early spring than during the sum- 

 mer. In consideration of the mussels as feeders on plankton ele- 

 ments, it is worth while to investigate whether these are not of 

 benefit to the lake as the reducers of excessive amounts of such 

 undesirable elements as Lyngbya, Aiuibaena and Microcystis, and 

 whether a considerable increase in the mussel population by means 

 of artificial propagation would not clear up the lake to a consider- 

 able extent. The following studies of stomach contents and table 



