ANATOMY OF THE CLAM. 



223 



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

 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 iip 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. loa. A. 3Iya arenaria with its siphons extended ; 



nal paSSCS thrOU2fh a in its natural position in the mud head-end downwards. 



-. , B, transverse section of Unio, showing the position of the 



dai'k rounded maSS, Bprinpr opening the shell. M, adductor muscle ; the ligro- 



, 1 . . inent represented by dark mass. C, section of Mya.show ng 



mostly Consisting Of the position of the spring to open the shell ; L, ligament. 



.i -i. j D, transverse section of Unio (after Brooks) ; 06, visceral 



tile llVer, COVereU eX- mass ; a, auricles ; t), ventricle, i, intestine: f, glandular 



fprillllv liv tlin nvarion part ofkldne y- z - non-glandular part of kidney ; y, sinus 

 lltlliy D}' LUC \ail an venosus ; /, inner, eg, outer, gills : m, mantle. 



