CERTAIN POINTS IN THE ANATOMY OF CHITON. 103 



hind border and the external opening of the bladder, it runs 

 outwards and then forwards (fig. 2_, p.k.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 Auodon, 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 uusegraented (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 ot 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 caeca are stated by von Jhering to be 

 ciliated. 



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

 receives no glandular cseca (fig. I, O to p.k.d.), is, with the 

 exception of a small portion adjoining the pericardial open- 

 ing, lined by columnar cells containing 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.k.d. to p.o.). Here are found 

 large columnar cells provided with long cilia, which line also 

 the pericardial opening. 



The cells of the glandular cseca seem to have the struc- 

 ture usually seen in moUuscan renal organs, and have been 

 correctly described by von Jhering. 



To sum up, the kidney of Chiton consists of — 



(1.) A duct opening to the exterior in the pallial groove 

 behind the generative opening, and internally into the 

 pericardium. 



(2.) Glandular cseca opening into this duct. 



The duct may be described as consisting of three parts : 



(1.) The part into which the glandular cseca of the kidney 

 open. This part is open behind where it opens to the 



