ANATOMY OF THE CLAM. 



243 



the sandy bottom of the water, when the mussel is plough- 

 ing its way through the A 

 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, but the spurt- 

 ing of water from the 

 clam's hole, observed 

 in walking over the 

 flats, is the stream eject- 

 ed from the siphon. 

 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 simple, un- 

 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- 



Fig. 161. A, Mya arenani with its siphons ex- 

 passes thTOUffh a tended; in its natural position in the mud head- 



end downwards ; B, transverse section of the shell, 

 showing the position of the spring opening the 

 shell; M, adductor muscle ; the lisarnent represent- 



dark rounded maSS, 



. se; , - 



mostly Consisting Of ed by dark muss ; (,', section of Unio, showing; the 



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



the liver, COVered ex- ment ; n. ideal transverse section of Unio; 7, intes- 



n 1 i/i . tine ; F, foot : V, ventricle ; A, auricle ; G, gills ; 



ternally by the ovarian , v . , nant ie ; s, sheii.-After Morse. 



