72 E. P. CHURCHILL, JR. 



of fat and it is such evidence that this paper is designed to set 

 forth. 



Mussels which had been kept in unstained fat solution will be 

 considered first. Camera lucida drawings were made of typical 

 portions of the sections, care being taken to indicate as far as 

 possible the number and position of the fat droplets. 1 In some 

 cases the fat was so massed together that individual droplets 

 were indistinguishable. Fat is represented in all the drawings 

 by heavy black dots or areas. 



The case of an adult specimen of Quadrula ebena which had 

 been kept in .001 per cent, fat solution for 15 days will first be 

 discussed. Sections of the gill filaments of this mussel were 

 prepared after fixation in a solution of osmic acid and Muller's 

 fixative. In such sections an abundance of fat droplets was to 

 be seen in the epithelial cells and a number in corpuscles in the 

 blood vessel in the interior of each filament (Fig. i, PI. I.). 

 Very few fat droplets were found in sections of the control 

 individual prepared by the same method (Fig. 2, PL I.). Frozen 

 sections, after having been stained with Sudan III., gave results 

 parallel to those just stated a large number of fat droplets in 

 the gill filaments of the mussels which had been kept in fat 

 solution for 15 days (Fig. 3, PI. I.), but practically nothing that 

 took the Sudan III. stain in the control individuals. The 

 epithelial lining of the water tubes of the gills of the individuals 

 which had been kept in fat solution was also quite crowded with 

 fat. In sections of the intestine of mussels which had been kept 

 in fat solution, fat droplets appeared in the epithelial lining. 

 Also in sections of palps and mantle fat droplets were revealed 

 but not in such abundance as was true in the case of the gills. 

 Fat droplets were quite numerous in the cells of the side of the 

 mantle next to the body but there were practically none in the 

 cells of the side lining the shell. The tissues of three adult 

 mussels which had been kept in fat solution for 15 days and of 

 two control individuals which had remained in filtered water for 

 the same period were examined by the two methods of preparing 



1 The term "droplets" will in this paper be applied to the spherules of fat found 

 in the tissues of the mussels which were studied. These droplets usually were of 

 diameters varying from 5 to 10 microns, though in frozen sections of the gills in- 

 stances were found in which the diameter was as great as 20 microns. 



