ANATOMY OF THE CLAM. 
223 
the sandy bottom of the water, when the mussel is plough- 
B 
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 m 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. 
of the mouth is a pair 
of flat, narrow-pointed 
appendages called pal- 
pi. The digestive ca- 
nal passes through a 
dark rounded mass, 
mostly consisting of 
the liver, covered ex- 
ternally by the ovarian 
On each side ¥ 
Fig. 155.—A, Mya arenaria with its siphons extended; 
in its natural position in the mud head-end downwards, 
B, transverse section of Unio, showing the position of the 
spring opening the shell. M, adductor muscle ; the li ra 
ment represented by dark mass. C, section of Mya,showing 
the position of the spring to open the shell; ZL, ligament. 
D, transverse section of Unio (after Brooks) ; ab, visceral 
Mass; a, auricles; v, ventricle , z, intestine ; ¢, glandular 
part of kidney ; z, non-glandular part of kidney ; y, sinus 
venosus ; zg, inner, eg, outer, gills ; m, mantle. 
