1881.] On certain Points in the Anatomy of Chiton. 125 



posterior tubules, which open into the dilated part of the duct and its 

 backward prolongation. The duct can be traced forward to about the 

 level of the 4th shell-plate (fig. 1, T), at which point it turns sharply 

 round and runs back parallel with the first part of its course. A con- 

 siderable part of the gland lies in front of this turning point of the 

 duct ; the secretion of this part is poured into a branch given off from 

 the main duct at the bend (fig. 1, T). The posteriorly directed part 

 of the renal duct lies close to the dorsal edge of the part running 

 forward, and, like the latter, receives the efferent ducts of bunches of 

 glandular caeca (fig. 1). From the level of the 5th shell-plate (fig. 1, O) 

 to its posterior termination (fig. 1, p.o.), about to be described, it 

 receives no glandular caeca, but runs backwards as a simple duct 

 distinguishable by its brown colour, which is due to a deposit of 

 colouring; matter in its walls. On reaching the level of the bladder-like 

 dilatation of the kidney duct first described, it applies itself to the dorsal 

 inner wall of that structure as far back as the level of the last gill. 

 At this point, which marks the hind border and the external opening 

 of the bladder, it runs outwards and then forwards (fig. 2, p.Jc.d.) in 

 close contact with the dorsal side of the lateral nerve cord. It runs 

 forward to about the level of the penultimate gill, where it suddenly 

 stops and opens by a small pore into the pericardium (fig. 1, p.o.) 

 beneath, i.e., ventral to the anterior part of the auricle. 



Comparing the arrangement of the kidney of Chiton with that of 

 Anodon, there is seen to be a close agreement. In both the kidney is 

 paired and consists of a gland bent on itself, opening at the one 

 extremity into the pallial cavity, and at the other into the pericardium. 

 In both the kidney is unsegmented (a fact to be remembered when 

 the nature of the shell and gills of Chiton is discussed). There is a 

 further agreement between these two animals in the relation of the 

 openings of the generative ducts to those of the renal ducts ; in both, 

 the latter are placed close behind the former. 



With regard to the minute structure of the kidney of Chiton, I 

 have no exact observations. It is necessary to study it in the fresh 

 state. The inner borders of the cells lining the glandular caejea are 

 stated by von Jehring to be ciliated. 



The most internal part of the kidney duct, i.e., that which receives 

 no glandular caeca (fig. 1, to p.Jc.d.), is. with the exception of a small 

 portion adjoining the pericardial opening, lined by columnar cells con- 

 taining a yellow colouring matter, which gives this portion of the duct 

 a yellow colour, easily visible to the naked eye. This yellow colouring 

 matter, which seems to be part of the excretion of the cells lining the 

 duct, is absent in the part of the duct which runs forwards from the 

 level of the hinder edge of the bladder to the pericardial opening 

 (p.Jc.d. to p.o.). Here are found large columnar cells provided with 

 long cilia, which line also the pericardial opening. 



