M4 WILLIAM RAY ALLEN. 



while touching cilia that lead in both directions, it obeys the 

 ciliary streams which lie uppermost and exert the greater force 

 upon it. 



Conclusions on the Function of the Ciliary Currents. 



The surfaces of the gills and of the upper part of the mantle, 

 and the contiguous faces of the labial palps, in fact, nearly all the 

 upper parts of the mantle chamber, have for their general purpose 

 the carrying of food to the mouth. The lower part of the mantle 

 chamber, upon which the heavier fragments are likely to fall, 

 are concerned principally with removing undesirable matter from 

 the animal. 



THE SELECTION AND REJECTION OF FOOD PARTICLES. 



Observers have differed widely in their notions of the ability 

 of the mussel to select its food. To me it is evident that there 

 are, to summarize, four points where such choice is exercised : 



(1) The labial palps, at the upper margin. 



(2) The labial palps, on the furrowed surfaces. 



(3) The mouth. 



(4) The incurrent siphon. 



As to the last, it is surrounded by a row of pointed, fleshy papillae, 

 having a resemblance to plant structures. These have two 

 sensory functions tactile and gustatory; for upon being dis- 

 turbed mechanically they are withdrawn into the shell, while a 

 continued teasing, or a strong chemical stimulus results in the 

 closing of the shell, or perhaps only the siphons. 



It is true that some material of no food value finds its way into 

 the alimentary canal. But the quantity is far smaller than if no 

 selection were made, and is of a harmless nature. All distinctly 

 injurious substances are rigidly excluded. 



That which has been rejected at the mouth, palps, or gill 

 accumulates upon the lower posterior margin of the mantle or 

 body wall, along with the collections made by these parts them- 

 selves, and is here massed in clots of mucus. When this has 

 attained considerable size the animal ejects it with a rapid 

 current of water, set in motion by a quick contraction of the 

 adductor muscles and closing of the shell (Figs. I and 2, r). 



