Respiration in Invertebrate Animals. 421 



tween the braucliise of these two classes exists. The horny chi- 

 tinous epithehum of the Crustacean contrasts obviously with the 

 fleshy, soft, and ciliated covering with which the MoUuscan 

 structure is invested. In the latter the blood-movement is aided 

 by muscular and vascular contractions. In the Crustacean the 

 flow of the blood is due almost exclusively to the action of the 

 heart, whose beats can be clearly read by the eye at the farthest 

 periphery of the circulation in the saltatory motion of the float- 

 ing corpuscles. In the walled contractile vessel of the Mollusk 

 no such evidence is discoverable. 



EXPLANATION OF PLATE XL 



Fig, L Respiratory chamber of Vermetus elegans laid open, after Quoy. 

 a, branchiae ; b, excretory ducts. 



Fig. 2. A single branchial conule of Chiton much magnified and newed 

 on its broad side, a, a, a, leaves ; b, base. 



Fig. 3. The former viewed edgewise, showing the axis (6) and the lateral 

 leaves [a, a, a). 



Fig. 4. A transverse section of the gill near the base, so as to exhibit the 

 main trunks artery {a, an'ow) and vein [b, arrow) in section. 

 e, e', secondary afferent and efferent trunks running along the 

 fixed border of the ultimate laminae {d, d'), in which the ultimate 

 vessels (c, c') are laid out. in parallel series. 



Fig. 5. A portion of the mantle of Patella vulgata detached and magnified, 

 sho\\'ing the gill-laminae, a, a, e, resting on a thickened ridge of 

 the mantle (b) ; d, tactile papillae ; c, c, line of the mantle. 



Fig. 6. A portion of the free edge of one of the branchial leaves, viewed 

 partly sideways in order to display the space (e, g) by which the 

 sheets of vessels a, i and b are separated; h. are the delicate 

 threads or trabeculce by which the component vascular layers are 

 held together ; /, the fleshy nodules to which the latter are 

 affixed. 



Fig. 7- expresses the course of a single ultimate branchial blood-channel 

 from the fixed border (a) of the lamina, round the free border (c), 

 back to the fixed border (6), proving the independence and con- 

 tinued individuality of the vessel ; e, the space circumscribed by 

 the loop (c) ; d,f, g. are the connecting thread and nodules. 



Fig. 8. exhibits one branchial leaf of Patella in situ ; it has a vaulted 

 figure, a, convex part ; b, concave ; c, the thickened border ; d, 

 the row of fleshy nodules next to the free border. 



Fig. 9. Outline sketch of the branchial system of Emarginula huzandi 

 (Cuv.). a, a, branchiae foliated on one side only ; b, notch in the 

 shell ; d, base to which the branchiae are attached ; c, rectal 

 intestine . 



Fig. 10. Outline sketch of the branchial system of Fissurella graeca. 



a, a, branchiae foliated o". both sides of the supporting axis ; 



b, perforation in the apex of the shell ; c, rectum. 



Fig. 11. Branchial and cardiac systems of Haliotis tuber cula. a. a , a, a , 

 branchiae doubly foliated ; b, b, the afferent trunks ; c, c, the 

 efferent ; d, d, the double auricles ; e, the single ventricle ; /, the 

 aorta; g, the rectal intestine. 



Fig. 12. Transverse section of the former. 



I To be continued.] 



