THE GILLS 



85 



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

 the posterior adductor. 



B. TheGilis. 



Cut away the right mantle-lobe completely with scissors, 

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

 of the gills, amd back along the attached base of the outer gill. 

 Take care not to da/mage the parts to which the mantle is 

 attached. 



Each gill consists of a pair of lamellae, united along their 

 ventral borders. Each lameUa is formed of very numerous 



Fig. 26. — 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 lyii)g. 

 AA, anterior adductor muscle. AW, anus. AB, right anterior retractor 

 muscle. ATT, right auricle. B, ligament of the shell. C, cloacal cavity. 

 CQ-, right cerebral ganglion. D, partition between the inhalent and exhalent 

 apertures. E, tentacles bordering inhalent aperture. P, foot. H, anterior 

 aorta. IG-, inner gill of right side. IP, inner labial palp of right side. 

 K, Mdney. IiM, left mantle-lobe. M, mouth. IT, posterior aorta. OQ-, 

 outer gill of right side. OP, outer labial palp of right side. P, right pro- 

 tractor muscle. PA, posterior adductor muscle. PC, pericardial cavity. 

 PG-, right pedal ganglion. PB, right posterior retractor muscle. B, rectum. 

 BM, llue of attachment of right lobe of mantle. "SiJS, space between right 

 and left lobes of mantle above the posterior adductor muscle. V, ventricle. 

 VM, visceral mass. 'W, edge of left mantle-lobe. 



