T7PE MOLLUSC A. 



291 



while another pair pass to a pair of ganglia lying below the 

 radula and in intimate connection with a peculiar subradular 

 organ, probably sensory, lying in this region. 



Fig. 130.— Diagram of Nervous and Excretory Systems of Chiton siculus 



(combination of two figures by Hallee). 

 an = anus. no = nephridial orifice. 



Br = ctenidia. oe = oesophagus. 



go = geuital orifice. pe = pedal nerve cord. 



n = nephridium. pi = pleural nerve-cord. 



As regards sense-organs, in addition to this subradular 

 organ whose function is entirely problematical, ridges of 

 sensory epithelium exist along the sides of the body in the 

 mantle-cavity. One such ridge runs along the inner wall of 

 the mantle-fold, while the other is found at the bottom of 

 the mantle-cavity passing over the bases of the branchial 

 plumes and sending a short prolongation outwards upon each 

 of these structures and seeming thus to correspond with the 

 osphradia of other MoUusca. 



