p 



and the hard parts are cast out by the upper or cloacal siphon, as waste. 

 The gills are, therefore, gatherers of food as well as purifiers of the blood." 

 Suspended between the gills we noticed a muscular body, which is 

 the abdomen, with the small, spade-like foot attached to the lower 

 end. This foot is capable of great expansion, and is thrust out through 



a round slit in 

 the mantle, the 

 edge of which 

 is very muscu- 

 lar and much 

 thickened. 



" Besides the 

 organs already 

 mentioned," 

 continued the 

 Professor, " the 

 clam has a ner- 

 v o u s system 

 like that of the 

 fresh-water 

 clam, a brown- 

 ish liver, and a 



heart and blood-vessels. The heart may be seen at the upper part 

 of the animal, where the mantle is very thin, and is like that of the 

 fresh-water clam. The foot is especially adapted for digging. When 

 not in use, it is a small projection on the anterior end of the abdomen; 

 but when extended ready for use, it is much swollen and greatly increases 

 in size. The animal digs by pushing the foot into the sand, thereby 

 making a hole, and pulling the foot after it." 



We asked the Professor if it was true that the clams were becoming 

 less numerous, and if so, why this was the case, as we had understood 

 that each clam lays thousands of eggs annually. He said that it was 

 true that the number was decreasing, and that this fact was clue to 

 several reasons; the first one being that they were gathered all the 

 year round, and were not given time enough in one year to make up 

 for the loss of the previous year. "And while it is true," he added, 

 " that each clam produces hundreds of thousands of eggs, yet they are 

 so beset with enemies that but a comparatively small number reach 

 maturity. The eggs are deposited during September and October, and 

 some of them are soon eaten by other animals. After the little clams 

 hatch, they swim about in the water for a time, and finally sink to the 



66 



Soft-shelled clam, with left valve and a part of the mantle removed 

 to show the principal organs of the animal. A, anterior end; P, posterior 

 end; aa, anterior adductor muscle; ah, abdomen; f, foot; ig, inner gill; 

 Ip, labial palpi; me, mantle edge, which is much thickened; og, outer 

 gill; pa, posterior adductor muscle; po, pedal oririce, through which 

 the foot is extended; sh, shell; s, siphons; u, urnbo. The arrows indi- 

 cate the direction of the currents of water. 



