



Fresh-water clam crawling over the muddy bottom 

 of a lake. Cl, cloacal siphon; Br, branchial siphon; F, 



foot ; S, shell ; B, surface of mud ; < , direction in 



which the animal is moving ; f I , currents of water 

 to and from the gills. (After Morse.) 



and we paused to watch them. The animal would stretch out its white, 

 fleshy foot to its fullest extent, get a purchase on the sand, and then pull 



the shell after it, sometimes 

 with a little jerk. In sev- 

 eral places the clams had left 

 a well-marked track in the 

 sand, showing the distance 

 which they had traveled. 



Professor Parker called 

 our attention to the two si- 

 phons which protruded from 

 the posterior end of the shell. 

 The lower one, he told us, 

 was taking in water filled 

 with microscopic plants and 

 animals, which the clam fed 

 upon, and also fresh oxygen 

 for the gills, or breathing organs. The upper siphon at the same time 

 was ejecting the waste products of respiration and digestion. 



About noon we stopped collecting and ate our lunch on a grassy 

 slope not far away, after which we proceeded to become better acquaint- 

 ed with these animals. Under the guidance of Professor Parker we 

 removed the right valve of the shell by cutting with a flat-bladed 

 knife through the large adductor muscles, and removing that portion 

 of the mantle which lies next 

 to and secretes the shell, we 

 then beheld the internal or- 

 gans of the animal. The in- 

 side of the shell was lined 

 by the soft mantle, which 

 was the exact form of the 

 shell. Its surface was cov- 

 ered with little cells, which 

 had the power of extracting 

 the carbonate of lime from, 

 the blood and building up 

 the shell with it. The 

 shelly skeleton of all clams 

 and snails is formed by a 

 mantle similar to this inside 

 of the shell. 



f 



Fresh - water clam with right valve and a part of 

 the mantle removed to show the principal organs of the 

 animal. A, anterior end ; P, posterior end ; ab, abdomen ; 

 b, anterior adductor muscle; br, branchial siphon; c, 

 posterior adductor muscle ; cl, cloacal siphon ; ct, cardi- 

 nal teeth ; d, anterior foot retractor muscle ; e, posterior 

 foot retractor muscle ; em, edge of mantle which forms 

 the pallial line ; f, foot ; h, protractor muscle of foot ; ig, 

 inner gill of right side ; 1, ligament ; Ip, labial palpi ; It, 

 lateral teeth ; m, mantle; mo, mouth ; og, outer gill of 

 right side ; s, shell ; u, umbo. 



