CHAFIER XXIV. THE FRESH-WATER MUSSEL. 

 (Anodonta cygncea.) 



1. Mode of Life. There arc several species of fresh- 

 water mussel, that known as the Swan Mussel (Anodonta 

 cygncea) being the commonest. In its mode of life it 

 shows a very close resemblance to Amphioxus, for it lies 

 habitually buried in the mud, with only a small portion 

 protruding. At this protruding end are two openings close 

 together (figs. 165 and 166) ; if a little colouring-matter is 



Fig. 165. SIDE VIEW OF ANODONTA. 

 (After Howeg.) 



put in the water near by, it can be seen io flow in at one 



of these openings 



from the other an outward 



current flows (exhalent opening). These constant currents 

 are maintained by ciliary action as in Amphioxus, the 

 inward current taking in both food and oxygen, the outward 

 taking out all waste products. Here again we shall find 

 a filtering apparatus by which the excess of water is allowed 

 to escape and oxygenate the blood as it does so, while the 



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