58 Our Food Mollusks 



path to the exterior is through the lower tube of the 

 siphon, and cilia could not possibly move the mass 

 against its powerful incoming current. 



When a sufficient quantity has collected, the clam 

 suddenly contracts the adductor muscles, the result being 

 that some of the water filling the spacious mantle cham- 

 ber is thrown out in a strong jet through the lower 

 siphon tube, and the waste material being in so favor- 

 able a position for it, is discharged. All bivalves seem 

 to have this habit of periodically discharging water from 

 the mantle chamber, and for the reason given. Long 

 neck clams, if steamed or baked immediately after be- 

 ing taken from their burrows, usually contain in the 

 mantle chamber a very annoying amount of sand. But 

 if they are allowed to stand over night in a bucket of 

 clean water, the sand is removed. In effecting its re- 

 moval, a large part of the water of the bucket will be 

 found on the ground where it has been thrown, some- 

 times to a distance of several feet, by the powerful jets 

 directed out of the siphons. 



Though there are always differences in details, the 

 mantle ciliation of all lamellibranchs so far examined 

 is practically like that of Venus. Apparently its sole 

 function is the removal of objectionable matter from 

 the body. 



The ciliary tracts of the side of the body are repre- 

 sented in Figure 14. Mud particles or fine sand grains 

 adhering to its surface are carried backward to the 

 point x, where they fall on the mantle, which disposes 

 of them as described. The figure also illustrates the 

 position of the labial palps and shows the striations or 

 ridges on the inner face of the posterior one, across 

 which food is carried to the mouth. 



