60 Descriptions of Preparations. 



themselves slowly along the furrow they thus form. The shape of 

 the ' foot^ varies much within the limits of the class^ from being- 

 exceedingly small or rudimentary, up to the proportions we see 

 here, where the name ' pelecypoda' has been coined to express its 

 shape and proportions. 



For a description of the digestive system of the Anodon, see 

 Langer, Denkschrift. Akad. Wiss. Wien. viii., 1S54, p. ig, 

 and Taff. i, and ii. figs, i, 2, and 9, or V. Hessling, Die 

 Perlmuscheln, p. 266. 



For that of Lamellibranchiata generally, see Huxley, English 

 Cyclopaedia, Article 'Mollusca/ p. 861. 



For a description of the organ of Bojanus, see Lacaze Duthiers, 

 Ann. Sci. Nat. Ser. iv. tom. iv. 1855, with semi-diagrammatic 

 figure, pi. V. fig. 2, which is reproduced by V. Hessling, 1. c. 

 pi. V. fig. 6. Langer, Denkschrift. Akad. Wiss. Wien. B. xii., 

 p. 39, 1856, tab. i., figs 3 and 4. 



20. Fresh-water Mussel (Anodonta C^jgnea), 



Prepared so as to show some of the functional as well as the anatomical relations 



of the mantle. 



A RED injection having been thrown into the auricles, has passed 

 not only into the gills, but also over the central portion of each 

 mantle lobe, from the line of attachment to it of the external gill, 

 down to the border where the central portion becomes continuous 

 with the free muscular rim of the mantle, and where it was at- 

 tached to the ' pallial line' in the shell. From the central portion 

 of the mantle, the injection has spread by anastomosis into tlie 

 vessels of the free muscular and tentaculate rim of the organ, and, 

 more freely, into the labial tentacles. Thus the functions of the 

 principal aerating organ, the gills, are seen to be more or less 

 supplemented by the subsidiary working of the structures specified. 



The mantle lobes are not united below the plane of the inferior 

 or neural surface of the two adductor muscles, except indirectly 

 by the commissural junction of the branchiae posteriorly to the 

 foot. By this junction of the gill plates the mantle cavity is divided 

 into two chambers, an inferior or branchial chamber, the entrance 



