104 ADAM SEDGWICK. 



exterior (fig. 1, D). In front it bends round (fig. 1, T), and 

 runs backward to about the level of the fifth shell plate, 

 where it changes its character, and is continuous with (2) a 

 duct (fig. 1, O) containing brown colouring matter in the 

 columnar cells lining it, and receiving no glandular caeca. 

 This part extends back to the level of the last gill, where it 

 turns outwards, and becomes continuous with (3) a part 

 running forward for a short distance close to the lateral 

 nerve, and lined by large ciliated columnar cells. This part 

 opens in front at the level of the penultimate gill into the 

 pericardium (fig, 1, p.o.). I expected to find the communi- 

 cation between the two parts of the renal duct behind in the 

 region of the bladder, and for some time I was puzzled at 

 not finding it. On mentioning the arrangement of parts 

 to Mr. Balfour, he suggested that the communication might 

 possibly be found in front, reasoning from the analogy of 

 the structure of the kidney in other MoUusca. On examin- 

 ing the anterior part of the gland more carefully, I at once 

 found that his suggestion was correct, the two parts of the 

 gland communicating as I have described. I have no obser- 

 vations to add to those of previous observers, on the general 

 arrangement of the nervous system. I may mention that 

 the lateral and pedal nerves have a coating of ganglion cells 

 and a central core of fibres. 



The animals are dioecious. The generative gland is 

 unpaired and dorsal. The generative ducts are paired, and 

 are attached to the hinder border of the gland, and open in 

 Chiton discrepans into the pallial groove between the thir- 

 teenth and fourteenth gill, in a line with the opening of the 

 renal duct. The duct passes dorsal to the anterior end of 

 the dilated part of the renal duct (fig. \, g.d.), and then 

 curls round the outer border of the lateral nerve cord to 

 its opening, presenting in this respect precisely the same 

 relation as does the renal duct. The male duct has a short 

 direct course to its opening (fig. 1), while the female duct 

 is much coiled. 



Another species. Chiton cancellatus, which I have examined, 

 presents essentially the same arrangement of its renal 

 organ and generative ducts as that just described for Chiton 

 discrepans. 



Dall^ states that in some species of Chiton the generative 

 products escape into the body cavity and make their exit by 

 several pores placed close together, and symmetrically, on 

 each side in the pallial groove; oviducts apparently being 



' ' Proceedings of the United States' National Museum,' vol. i. 



