SENSE-ORGANS OF CHITON. 



145 



been discovered by Moseley,* tliey are even more 

 numerous. Chiton itself, indeed, Las none; but in 

 Scliizocliiton there are 300, and in Corephium more 



Fig. 98. Schematic representation of the soft and some of the hard parts in a shell of 

 a Chiton (Acanthopleura), as seen in a section vertical to the surface, and with the 

 margin of the shell lying in the direction of the left side of the drawing, a. 

 Conical termination of sense-organ ; h, l>', ends of nerve ; c, nerve ; /, calcareous 

 cornea ; g, lens ; h, iris ; k, pigmented capsule of eye ; m, body of sense-organ cut 

 across ; n, nerve of eye ; p, nerve of sense-organ ; r, rods of retina. 



than ten thousand. As in Onchidium, they probably 

 arose as modifications of the organs of touch, and are 

 supplied by the same nerves. They possess (1) a 

 cornea, (2) a perfectly transparent and strongly biconvex 

 lens, and (3) the retiDa, which presents a layer of short 

 but well-defined rods. It is interesting that they point 

 towards the light, and not, as in Onchidium, away 

 from it. 



* " On the Presence of Eyes in Shells of certain Chitonida3," 

 Quarterly Journal of Microscopal Science, 1885. 



