C88 



ZOOLOGY 



of the mantle : the inner lamella of the inner lamina is also attached 

 to the visceral mass in front (A), but is free further back (B). The 

 gills are longer than the visceral mass, and project behind it, below 

 the posterior adductor (C), as far as the posterior edge of the 



Fin. [iG8. — Anodonta cygnea. Three transverse sections, A. B.C. au. aimcle ; bl. urinary 

 bladder ; ext. (jl. external gill-lamina ; ft. foot ; i. l.j. inter-lamellar junction^ int. intestine ; 

 int. gl. internal gill-lamina; A-rf, kidney ; A-, o. Keber's organ ; Zf/. ligament ; m. mantle ; 33. ad. 

 posterior adductor ; pc. pericardium ; ret. rectum ; s. hrc. supra-branchial chamber ; sh. shell ; 

 ^?/- typhlosole ; v. ventricle; vc. vena cava; v. f/n. visceral ganglion. (After Howes, slightly 

 altered. 



mantle: in this region the inner lamellae of the right and left 

 inner laminae are united with one another, and the dorsal edges 

 of all four laminae constitute a horizontal partition between the 

 paliial cavity below and the exhalant chamber or cloaca above., 

 Owing to this arrangement it will be seen that the water-tubes all 



