AlTATdMr OF THE OLAM. 



the sandy bottom of the water, when the mussel 

 ing its way through the 

 sand with its tongue- 

 shaped foot, which is a 

 muscular organ attach- 

 ed to the visceral mass, 

 and is a modification 

 of the under lip of the 

 larval mollusk. In the 

 foot is an orifice for 

 the passage in and out 

 of water, and the spurt- 

 ing of water from the 

 clam's hole, observed 

 in walking over the 

 flats, is the stream thus 

 ejected from the foot. 

 The inflowing currents 

 of water pass from the 

 inner end of the mus- 

 cular siphon below the 

 lenticular visceral mass 

 to the mouth, which is 

 situated at the anterior 

 end of the shell, oppo- 

 site the siphon. The 

 opening is simijle, u.n- 

 armed, without lips, 

 and often difficult to 

 detect. On each side 

 of the mouth is a pair 

 of flat, narrow-pointed 

 appendages called pal- 

 pi. The digestive ca- 

 nal passes through a 

 dark rounded mass, 



243 



Fig. 161.—^, Mya arenaria with its siphons ex- 

 tended ; in its natural position in the mud hoad- 

 end downwards ; B, transverse pcction of the shfll, 

 showing the posilion of the sprinc; openint: the 

 - . „ shell; iT/, adductor miipcle ; the lio'ament renresent- 



niOStly COnSlStinj^ OI ed hy dark mass ; f^. section of Unio, ehowincr the 

 ., -. J position of the spring to open the shell; L.liga- 



tne liver, covered ex- ment ; />. ideal transveri^e section of Unio; /, intes- 

 , nil! • tine; Jf", foot; V, ventricle; A, auricle: G, gills: 



tenially by the ovarian at, mantle ; S, ehell.— After Morse. 



