020 R. J. HARVEY GIBSON ON THE 



horizontally, the broader end being anterior. The duct connecting it with the 

 cavity of the kidney is comparatively short and wide, and like that of the left 

 kidney is lined by squamous epithelium, and surrounded by connective tissue 

 and muscle. The duct soon opens into the subanal tract of the right nephridium, 

 and then becomes lined by granular ciliated epithelium similar to that found in 

 the left kidney. The histological structure of the right kidney is similar in 

 all respects to that of the left, but the cells are filled with granules which are 

 much darker in colour, though they can scarcely be said to be more numerous. 



While the left nephridium partakes more of the nature of a sponge, the right 

 is rather a sac with plaited walls (PL CL. fig. 34). 



With regard to the comparative structure of the two kidneys, the author is 

 inclined to think that the substances which the right kidney secretes from the 

 blood are chemically different from those secreted by the left. The degree of 

 solubility in certain reagents of the granular matter of the two kidneys is 

 different, and the granules are much darker, in addition to being more numerous 

 in the right than in the left. This subject will, however, be gone into in 

 detail in the physiological part of the work. 



Cuvier (loc. cit.) asserts that the lamina? dependent from the mantle arc 

 gills. Blainville denies this, and thinks the mantle over the neck is respira- 

 tory in function, owing to the number of vessels found there. Adamson, 

 Milne-Edwards, and Gray support Cuvier's view. As above shown, both 

 views are to be accepted as true. Dall {Amer. Jour, of Conch., 1871, 268)> 

 strangely enough, says that the cordon of gills is uninterrupted; an undoubted 

 interruption does take place at the point of entrance of the branchial vein over 

 the left shoulder (PI. CLI. fig. 38). Lankester {Ann. and Mag. Nat. Hist., iii. 

 p. 20, 1807), showed that Patella had two distinct kidneys, one of which, he was 

 at that time able to show, opened into the pericardium. The opening into the 

 right kidney was subsequently discovered by Lankester and Bourne, and the 

 existence of the subanal tract pointed out {Ann. and Mag. Nat. Hist., vii. 1881). 

 Doubt being thrown by various observers upon certain points in Lankestku's 

 description, more especially on the connection between the left kidney and 

 the pericardium, the subject was reinvestigated by Cunningham {Quart. Jour. 

 Mic. Science, xxii. 309), who further described the form and structure of the 

 renal organs, and confirmed Lankester's account. Williams' account of the 

 structure of the branchiae (as quoted by Dall in Amer. Jour. Conch., 1871) 

 the author is able to confirm and extend ; the author found, however, no indi- 

 cation of the cilia mentioned by Williams as covering the branchiae ; nor are 

 they, indeed, to be expected there, since the laminae are really outpushings of 

 the mantle wall, and not morphologically true gills, as in the cited case of the 

 gill plate of Anodon. 



5. Connective Tissue System. — The connective tissue of Patella does not call 



