98 



THE FRESHWATER MUSSEL. 



Insert a seeker into the anus and pass it upwards and 

 forwards along the rectum as it lies on the dorsal surface of 

 the posterior adductor. 



B. The Gills. 



Cut away the right mantle-lobe completely with scissors, 

 cutting along the base of the palps, round the anterior end of 

 the gills, and back along the attached base of the outer gill. Take 

 care not to damage the parts to which the mantle is attached. 



Fig. 28. Anodonta cygnea. Diagrammatic view from the right side. 

 The right valve of the shell and the right mantle-lobe have been 

 removed, and the pericardial cavity opened from the right side. 

 The line of attachment of the right mantle-lobe is indicated by the 

 strong dotted line. (a. m. m.) 



A, margin of the left valve of the shell in which the animal is lying. AA, 

 anterior adductor muscle. AN, anus. AR, right anterior retractor muscle. 

 AU, right auricle. B, ligament of the shell. C, cloacal cavity. CG, right 

 cerebral ganglion. D, partition between the inhalant and exhalant apertures. 

 E, tentacles bordering inhalant aperture. F, foot. H, anterior aorta. IG, 

 inner gill of right side. IP, inner labial palp of right side. K, kidney. LM, 

 left mantle-lobe. M, mouth. N, posterior aorta. OG, outer gill of right side. 

 OP, outer labial palp of right side, p, right protractor muscle. PA, posterior 

 adductor muscle. PC, pericardial cavity. PG, right pedal ganglion. PR, 

 right posterior retractor muscle. R, rectum. RM, line of attachment of 

 right lobe of mantle. RN, space between right and left lobes of mantle above 

 the posterior adductor muscle. V, ventricle. VM, visceral mass. W, edge of 

 left mantle-lobe. 



