THE ABSORPTION OF FAT BY FKESEI-WATER MUSSELS. 75 



been stained with Sudan III. will now be considered. Before 

 beginning the experiment the valves of the shell were opened 

 sufficiently to permit the observation to be made that the tissues 

 of the animal to be experimented with were of normal color and 

 condition. The mussels were then kept in stained fat solution 

 for periods varying from 5 to 15 days. At the expiration of 

 these periods the gills of the adult and the gills, mantles and foot 

 of the juvenile animals were found to be red or pink in color. 

 Sections of the gills of such adult mussels were prepared by the 

 freezing method. In these sections pink colored fat droplets 

 were found within the epithelial cells of the gill filaments and of 

 the water tubes (Fig. 15, PI. I.). This fact furnishes additional 

 proof of the absorption of fat from the solution. It renders 

 negligible the consideration that the heavy loading of fat found 

 in each case in the mussels which had been kept in the fat solu- 

 tions might have been due to the chance use of an extraordinarily 

 fat individual. Some of the juvenile mussels which had taken 

 on a red color while they had been kept in the stained fat solution 

 were then transferred to filtered water. The color remained 

 visible in the foot and gills for more than a week in some cases. 

 This would tend to show that the red colored fat was absorbed 

 and oxidized within the organism and that the red color was not 

 due merely to the adherence of the stained solution to the 

 surface of the gill or foot. 



In all, including those mussels which were kept in stained and 

 unstained fat solutions and the control individuals, the tissues of 

 twelve mussels were examined. The sections all revealed much 

 fat within the tissues of the mussels which had been kept in the 

 fat solutions and very little or none in those of the control 

 individuals. Consideration of the above results leaves no doubt 

 of the fact that fat may pass from a fat solution into the body 

 of the mussel. Now there remains the question of whether it is 

 all absorbed through the intestine or partly through the tissues 

 of the outer body walls. Experiments intended to throw light 

 upon this question were undertaken with juvenile mussels. 

 These had been kept in water containing little food for several 

 weeks so that their tissues contained little stored fat at the 

 beginning of the experiment. 



