THE RESPIRATORY SYSTEM. 875 
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= 
Fig. 306. 
Fie. 307. 
Fie. 306.—Vertical transverse section of fresh-water mussel (Anodon) through heart (after 
Huxley). V, ventricle ; a, auricles; 7, rectum ; p, pericardium ; 7, inner, 0, outer gill; 
o’, vestibule of organ of Bojanus, B ; f, foot ; m, m, mantle lobes. 
Fie. 307.—Gill of fish (perch), to illustrate relations of different blood-vessels, etc., concerned 
in respiration (after Bell). A, branchial artery ; B, branchial arch seen in cross-section ; 
V, branchial vein ; a, v, branches of artery and vein respectively. 
Comparative.—It is hoped that the various figures accompa- 
nied by descriptions, introduced in this and other chapters, will 
make the relations of the circulation and respiration in the va- 
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Woo EVI x x! xu fox xv 
Fic. 308.—Diagram of scorpion, most of the appendages having been removed (after Huxley). 
a, mouth ; 6, alimentary tract; c, anus; d, heart; e, pulmonary sac: f, position of ven- 
tral ganglionated cord ; g, cerebral ganglia; T, telson. VII—XX, seventh to twentieth 
somite. IV, V, VI, basal joints of pedipalpi and two following pairs of limbs. 
