Respiration in Inverteh'ate Animals. 257 



Fig. 3. Enlarged view of a single branchial leaflet of the Periwinkle : 

 a, a, cartilaginous thick or dorsal edge ; b, b, folds or second- 

 ary plications of the surface of the leaflet; (B), the same in sec- 

 tional view, showing that tlie plicce exist on both faces of the leaf; 

 c, c, a second set of i)lic!t ; h, h, the blood-ehannels as tht'v course 

 in a parallel order towanls the free margin (</), at which place 

 they loop round as shown in fig. 5 ; (/, d, (rig. 'A) indicate the 

 fi.\ed border of the lamina where the afl^erent and efterent trunks 

 are situated; j, the extreme tapering eml of the lamina. 

 Fig. 4. Four branchial leaflets from the gill of Buccimim undutum, with a 

 portion of tiie roof from which they depend : a, a, the dorsal or 

 cartilaginous border of the lamina; a,/, rows of cilia on the 

 same ; e, c, section of roof to whicii they are attached ; d, d, the 

 flat surface or face of the leaflet, traversed by wavingly parallel 

 blood-channels ; a, b, g, the free border at which these channels 

 loop, so as to reach the opposite face ; c, c, the attached base at 

 which the afferent and efferent trunks are placed. 



Fig. 5. is a small portion of the free border, b, of the last figure, highly 

 magnified, showing the mode in which the blood-channels, g, 

 curve round the free border in passing from one face of the 

 lamina to the other. 



Fig. 6. A small portion of the e])ithcliura from the face of the lamina. 



Fig. 7. The hyaline cartilage which gives rigidity to and is enclosed iu the 

 substance of the dorsal border of the lamina. 



Fig. 8. Two epithelial ciliated scales from the free margin, b, of fig. 4. 



Fig. 9. a, a, a, a, a, a, six leaflets from the gill of Purpura Lapillus : 

 a', shows the hook-like manner in which the dorsal border curves 

 at the point — a contrivance which increases the elasticity of the 

 cartilage in luifurling and tightening the lamina ; c, marks the 

 course of the blood-channels across the area of the leaf; b, is the 

 free or floating border ; d, the base ; b, the base of the cartila- 

 ginous border. 



Fig. 10. is a diagram of the entire gill in Purpura Lapillus, showing the 

 general form of the organ, the largest and longest laminfe being 

 in the middle, the smallest at either end. 



Fig. 12. The hyaline cartilage from the dorsal border of the gill-leaf of 

 Purpura Lapillus. 



Fig. 12 b. One of the blood-channels from the same, traced at the free 

 border, showing the mode in which it loops. 



Fig. 13. Seven branchial laminae from the gill of Trochus magus: a, car- 

 tilaginous border ; d, base of the same ; e, face of the lamina in- 

 dicating the course of the blood-channels ; b, free border ; c, base. 



Fig. 14. Seven leaflets from the gill of Trochus cinerarius: a, d, cartila- 

 ginous border ; b, free border ; c, denotes the directions of the 

 muscular fibres which are attached to the base of the hyaline car- 

 tilage ; e, e, base. 



Plate XI. 



Fig. 1. Limax niger, showing the roof (a) of the respiratory chamber re- 

 flected. On its under surface (6) is seen a plexus of vessels, 

 which are more distinct on the pericardium (c) ; c', c', represent 

 the mucous gland ; d, heart ; g, vessels distributed over the floor 

 of the respiratory chamber ; e, orifice of the breathing-chamber ; 

 h, aorta. 



Fig. 2. A small portion of the vascular plexus from the breathing-cavity 

 of the preceding specimen, magnified, exhibiting the tendency to 

 Ann. i^- Mag. N. Hist. Set. 2. Vol.wW. 17 



