r88 



EYES OF CHITON 



CHAP. 



they are arranged symmetrically in rows diverging from the 

 apex of each plate, but in old specimens the eyes towards the 

 apices are generally rubbed off by erosion or abrasion. Moseley 

 regarded the occurrence of scattered eyes as indicating an origi- 

 nal stage of development, when the eyes were at first disposed 

 irregularly all over the surface of the shell ; the gathering into 

 regular rows showing a later stage. 



The eyes appear to be invariably more numerous on the 

 anterior plate. Thus in Corephium aculeatum there are about 



-Xai^tu-^icjs. 





Fig. 92. — Dorsal eyes 

 of Chitonidae, show- 

 ing the various forms 

 of arrangement in 

 the first and fourth 

 valves of 1, la, Acan- 

 thopleura spinigera 

 Sowb., E. Indies, X 

 2; 2,2«, To7iicia siie- 

 zensis Reeve, Suez, 

 X 3; 3, 3a, Acan- 

 thopleura granulata 

 Gmel., W. Indies, 

 X 2; 4, 4a, Tonicia 

 lineolata Fremb., 

 Chili, X 2. From 

 specimens in the 

 Museum of Zoologj^, 

 Cambridge. 



12,000 in all, of which more than 3000 are on the anterior 

 plate. In Schizochiton they are arranged in very symmetrical 

 rows, six of which are situated on the anterior, and only two, 

 sometimes only one, on the central plates. In Tonicia mar- 

 morata the eyes are sunk in little cup-shaped depressions of 

 the shell, possibly to escape abrasion. As regards shape and 

 size, in Ch. incisus they are circular, and about -^^ inch in 

 diameter, this being the largest size known ; in Ch. sinniger 

 and Ch. acideatus they are oval, measuring about ^^^ x -^^-^ inch. 

 There are no eyes in Chiton proper, nor in Mopalia^ 3Iaugeria^ 



