7O E. P. CHURCHILL, JR. 



discussed in the latter part of this paper; to Dr. G. L. Houser 

 for the use of several books and a microscope from the laboratories 

 of the University of Iowa; and to Dr. R. E. Coker for aid ren- 

 dered while the work was being carried on at the Fairport 

 Laboratory. 



MATERIALS AND METHODS. 



The mussels upon which the investigations were carried out 

 were individuals selected from the more common species found 

 in the Mississippi River near Fairport, Iowa. Both adult and 

 juvenile specimens were employed. Care was exercised to 

 choose for the experiments non-gravid mussels which were in a 

 seemingly healthy condition, "shoulder-raked" or hand collected 

 individuals being generally used in preference to those dragged 

 out of the water by "crow-foot" hooks. 



The water used in the experiments w T as that of the general 

 supply for the Fairport Laboratory which had come from the 

 Mississippi River through a filter which removed the mud and 

 at least the greater part of the living animal and plant organisms. 



The fats employed were those of olive oil and cottonseed oil. 

 The results were the same in both cases as far as could be observed. 

 The oils were saponified by boiling with sodium hydroxide, the 

 resulting solution being diluted to strengths varying from .001 

 per cent, to .005 per cent, in different cases. This method can 

 be used only with freshwater animals as the soap is precipitated 

 from the solution in salt water. 



The adult mussels experimented with were kept in glass aquaria 

 containing about 5,000 c.c. of the fat solution of the desired 

 strength. The bottoms of the aquaria were covered to a depth 

 of an inch or two with coarse sand. Control individuals were 

 run side by side with the experiments in similar aquaria contain- 

 ing filtered water only. The juvenile mussels were generally kept 

 in smaller aquaria. In the cases of experiments extending over 

 more than twenty-four hours, the solutions were changed daily, 

 no effort being made to balance the aquaria. As the mussels 

 from the river are accustomed to a current of water this seemed 

 to be the closest approximation to natural conditions which it 

 was possible to obtain in the laboratory. 



The tissues of various portions of the adult animals experi- 



