14 ^ NEW YORK STATE MUSEUM 



much mud is entering, large quantities of it must be collected on 

 the gills and be sent forward toward the mouth. I have spoken 

 of the fact that the palps are capable of extended movements. If 

 they are withdrawn so as not to touch the gills, material will 

 accumulate in the anterior parts of the gill grooves till masses are 

 formed so large that they fall off into the space of the mantle 

 chamber below — perhaps to be taken up by the currents on the 

 mantle. At any rate, they would be discharged when the mantle 

 space was emptied. I have no doubt, especially after what I have 

 observed in forms like Yoldia, that the palps of Venus are from 

 time to time withdrawn from contact with the gills, in order 

 that they may receive no material from them. 



It is when we come to examine the palps that we find the most 

 complex arrangement for keeping material from entering the 

 mouth when that is desirable. A close examination of the inner 

 faces of the palp shows a narrow strip around its margin which 

 is without the ridges previously described. Both of these margins 

 are very densely ciliated. When suspended material falls on the 

 upper margin, it is carried up onto the surface of the ridges [fig. 

 2, urn] and across them to the mouth. Anything which touches 

 the other margin, on the other hand, is swept with great rapidity 

 in the other direction — out to the end of the palp, where it 

 accumulates and is finally thrown off into the mantle chamber 

 below. It is true that this margin is narrow, and not much 

 material suspended in the water would strike it; but probably 

 when a large quantity is collected on other parts of the palp, 

 this edge is folded over so as to touch these heavily laden sur- 

 faces, and sweeps them clean. 



It thus appears that there are extensive ciliary tracts for collect- 

 ing and conveying food to the mouth; but that, in addition to 

 these, there are other ciliated surfaces by means of which unde- 

 sirable material may be excluded without the necessity of closing 

 the shell. Because of the advantage of sustaining the 

 aeration of the blood, this must be of very great service when the 

 water is muddy. 



In this description of the feeding habits of Venus many 

 important details have been omitted, particularly in regard to the 



