FEEDING HABITS OF FRESHWATER MUSSELS. 133 



material gathered by both gills and by the dorsal part of the body 

 epithelium and mantle must finally reach one of the three ad- 

 jacent points (i) the mantle just above the palps, (2) the body 

 wall just opposite the first point, or (3) a point on the edge of the 

 inner gill just above the labial palps. All these are within easy 

 reach of the palps (Figs. I, 2, 4, and 6). 



No one, to my knowledge, has succeeded in inducing a mussel 

 to behave normally, after the shock of removing parts of the 

 shell and mantle in order to observe the palps at work. But I 

 have repeatedly obtained the reactions which occur. When the 

 palps lie in contact with either body, mantle, or gill, their collec- 

 tions of material pass between the palps and mouthward. Other- 

 wise such material is carried on down by the several structures 

 and discarded. The fact that the upper margins of the labial 

 palps adhere to each other and form a trough (Figs. 4 and 6) 

 makes it possible to reach at least two of the three sources of 

 supply simultaneously. 



Since we have the mechanism for such a method, and since the 

 reactions, though fragmentary and under abnormal conditions, 

 are of a confirmatory nature, we may safely infer that the labial 

 palps do actually accept or refuse food, either through reflex 

 stimuli or in response to volition. 



The Function of the Mucus. 



The entire epithelium touching the branchial chamber is 

 abundantly supplied with glands which secrete a mucous sub- 

 stance (Siebert, I.e.). The mucus envelops and binds together in 

 strands the material to be transported by the cilia. This is 

 particularly true of those particles which are of a very distasteful 

 nature. That this secretion is dependent on local reflexes is 

 quite evident from the fact that it may be stimulated in an organ 

 entirely severed. 



It is this collection of food in a film of mucus, which makes 

 possible the mechanism of the furrowed surface of the labial 

 palps. If each particle were manipulated independently, it 

 would tend to eddy back and forward between the opposing 

 streams of cilia, and considerable confusion might result. But 

 a strand of material spans the summits of several ridges, and 



