S6 On the Mechanwn of Aquatic Respiration. ^'' 



-fi9 gj/ia-nsiphoij ; b, b, extra-branchial or inhalent siphon ; b, 6, b, ])aUia{ or 



9i{j z:AiH(ii extra-branehial cavity ; c, external or inferior branchial lamella ; 



-iim6'Srr^ d, internal or superior lamella; e, membrane tying the attached 

 border of the superior branchial lamella to the side of the foot and 

 visceral mass, rooting the i/ifm-branchial or anal chamber (/) ; the 

 aiTows (g) show the currents descending from the branchiae into 

 the anal chainber, and thence out through the excurrent siphon, 

 >« ,'> , i under the membranous roof (/) connecting the branchiae of the 



t-yflsiv '' two sides ; h, mouth; i, i, palpi. The arrows indicate the direc- 

 '•■ ■> " tion of the currents. 



Fig. 7. is a transverse ideal section of the preceding figure. It exhibits the 

 relation of the water-currents and cavities : a, incmTcnt siphon, 

 leading (at a') into the extra-branchial or pallial chamber d, d ; 

 b, excurrent siphon leading out of (at U) the intra-branchial or 

 anal chamber c ; e, e, e, e, branchial lamellae. 

 Fig. 7'^. One-half of Mytilus (tig. 10) in transverse section, showing the 



K» ttstn^^^v mode in which the branchial lamellae are attached to the raan- 



' ^ ;, ;tle h,h; a, b, branchial lamellae of one side ; c, c\free proximal 



- " ' border of res])ectively the upper lamella of the internal gill-plate, 



and the lower of the external. The attached lameUae {d, d') of each 



gill-plate are joined by a membrane at e; ^, shows the continuous 



membrane which at the proximal borders connects the branchial 



^j bars, so that at this point no water can permeate the lamella; 



t nV, f,f\ denote the spacious grooves which receive the water from 



Jii ; 2^i'' t\\Q interlamellar tubes and convey it to the cloaca. The arrows 

 mark the direction of the currents. t>U nasif 



s-i.!\?:^-':_ : •(•;, jMih! - Plate II. 



■^F%r. 8. Vertical viev^ b?^tl^ common Cockle, showing the relation of the 

 Aykpodi , "branchial system to the siphons and cavities : a, excurrent siphon 

 yjdt III leading out of the anal cavity (a'} surrounding the visceral mass (») ; 

 b3ltji"orT ^' incurrent siphon conducting (at b') into the extra-branchial 

 ^ cavity (c) ; e, arrows marking the excurrent currents coming from 



the branchiae ; g, palpi ; /, mouth. 



Fig, 9. Ideal transverse section of the former figure : a, excurrent siphon 



, f":ryn : leading out of the anal cavity (e) at a' ; b, incun-ent ditto opening 



edi' ni I ^^ ^' ^^^^ ^^^ general cavity of the mantle (c, c) at 6'; d, d, bran- 



• „ chiae;/, the line of the mantle uniting the branchial lamellae 



together. The arrows show the order and tendencies of the water- 

 -iJlXOO- a- currents. 



bS^f.^Oi Vertical view of Mytilus, exhibiting the systems of respiratory and 

 ^i'p.am B alimentary water- currents : a, mouth ; i, i, palps ; b, extra-bran- 

 doifiw m ^^^^^ ^^ pallial cavity ; c, two longitudinal halves of the rectum, 

 [± j^ terminating in the excurrent channel in the mantle ; e,ehf, sur- 

 ,9iJgin// j.oun(^e(j by the grooves (c) indicated by the arrows which convey 

 JB '^til'li) the expiratory water from the branchiae in the direction of the 

 JO ffSVQr- cloaca ; d, d', branchial lamellae ;j, j, arrows showing the direction 



of the currents along the distal ov free border of the gills which 

 ^ -tftir Pi' convey food to the mouth. 



vFtjr. li. Ideal transverse section of the former — compare with fig. 7^. PI- I- 

 o w J ? ■ ! - It ig designed only in outline plan to display the relative anatomy 



of the extra-branchial (6), the branchiae and pallial membrane {d), 



and the intra-branchial or anal chamber (c) ; a, openings of the 



mantle. 

 , jRia. 12. Oyster: a, mouth ;betvveen the palpi ; 6, anus, emerging out of 

 ' - s ' the visceral mass; c, upper half of the mantle arching over the 



