rv. 



bladed knife, removed the left valve, and presented to our wondering 

 gaze the animal which made the shell. 



We saw that the shell was lined by a soft skin, called the mantle 

 or pallium, which secreted the two valves. This formed a closed bag, 

 with the siphons at one end and a round aperture at the other end 

 through which the foot might be thrust. 



Carefully cutting away the central transparent part of the mantle, 

 the Professor laid bare the internal organs of the animal, and explained 

 their functions to us in detail. The long siphon was seen to contain 

 two canals and to be very elastic, as we had seen 

 in the living animal, being capable of stretching 

 out several times the length of the shell. The 

 aperture was seen to be lined with hairs, or cilia, 

 which keep up a constant motion in the living 

 clam, creating an inward current, which brings 

 food to the animal in the form of microscopic 

 animals and plants. 



This class of mollusks, like the fresh-water 

 clams, is headless, and the mouth leads directly to 

 the stomach. Just back of the posterior adductor 

 muscle, we were shown two pairs of delicate or- 

 gans, suspended from the dorsal part of the ani- 

 mal, and called the labial palpi, or lips, which 

 protect the mouth; and which, by the motion 

 of the minute cilia on their surface, create a current of water toward 

 the mouth. Lifting up the palpi we saw the little mouth lying between 

 them. The most conspicuous objects were the two pairs of gills ; one 

 pair lying on either side of the fleshy abdomen. The gills were broad, 

 wrinkled masses, hanging from the dorsal part of the animal to which 

 they were attached. They were filled with many little tubes, through 

 which the blood circulates, expelling its poisonous carbonic acid gas, 

 and becoming laden with fresh oxygen. 



"The gills not only purify the blood," said Professor Parker, "but 

 they also aid in gathering the food. If examined with a powerful 

 magnifying glass, the surface of the gills will be seen to be covered 

 with thousands of little hair-like cilia all moving in unison like the 

 oars of a man-of-war boat, thus keeping up a constant current. The 

 little animals and plants which are brought in through the lower, or bran- 

 chial siphon are caught upon the little cilia, rolled into a mucilaginous 

 string, and passed on to the mouth, where they enter the stomach and 

 intestine, and are digested. The nutritious portion is absorbed in the blood, 



65 



Diagram of a section of the 

 soft - shelled darn, showing 

 method of opening and clos- 

 ing the valves, ch, chondro- 

 phore, or shelly depression 

 for the cartilage, or resili- 

 um, r ; Iv, left valve; rv. right 

 valve; m, adductor muscle; 

 u, um bo. 



