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MANUAL OF ELEMENTARY ZOOLOGY 



of flaps which hang down on each side of the body. 

 One pair is large, extends from the hind end along the 

 greater part of the length of the animal, and consists of 

 the gills. The other is smaller, lies in front of the gills, and 

 is known as the labial palps. The foot is a compressed 

 structure, with a point directed forwards, lying under the 

 front half of the body. Its lower part is muscular, its 



g'e n . 

 I. p. ; h.o. I -ml. 



l.o.g. 



a.ad, 1 



>:i.y. 



Fig. 223. — A swan mussel removed from its shell and lying on its right 

 side with the left mantle lobe and left gills turned back. A portion 

 of the inner lamella of the left inner gill has been cut away to show 

 the openings of the kidney and gonad. 



a.ad., Anterior adductor muscle ; d.s., dorsal siphon ;_A, foot ; gen., opening of the 

 duct of the gonad ; k.o. , opening of the kidney ; l.i.g~., left inner gill ; /.«//., left 

 mantle lobe; l.o.g;., left outer gill; /./.. labial palps; r.i.g~., right inner gill; 

 r.inL, fight mantle lobe; r.ml ., thickened edge of the same; r.o.g., right 

 outer gill ; V.S., ventral siphon. 



upper part soft, containing the genital organs and intestine. 

 It is thrust out between the valves by the forcing of blood 

 into the sinuses which it contains, and withdrawn by the 

 removal of the blood by the action of its muscles. In 

 locomotion it is wedged into the mud or between stones, 

 and the body is then drawn forwards upon it by the 

 retractor muscles. Above the foot, between it and the 

 anterior adductor muscle, lies the mouth, bordered by 

 upper and lower lips. At the sides of the mouth these lips 



