i88 



EYES OF CHITON 



symmetrically in rows diverging from the apex of each plate, Itut 

 in old specimens the eyes towards the apices are generally 

 ru1;)bed off hy erosion or alirasion. Moseley regarded the occur- 

 rence of scattered eyes as indicating an original stage of develop- 

 ment, 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 he invariably more numerous on the 

 anterior plate. Thus in CnrqiJi.iion aculcatum there are aliout 



Fig. 92. — Dorsal eyes of 

 Chitonidae, showing 

 the various forms 

 of arrangement in 

 the first and fourth 

 \a\ve.iioi\,\a,Acan- 

 thopleura spiniyera, 

 Sowb., E. Indies, x 

 2 ; 2,2a,Toniciasue- 

 zensis Eeeve, Suez, 



X 3 ; 3, 3a, A can- 

 thopleura gra n vlata 

 Gmel. , W. Indies, 



X 2 ; 4, 4a, Toiiicia 

 Uneolata, Fremb., 

 Chili, X 2. From 

 specimens in the 

 Museum of Zoology, 

 Cambridge. 



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

 plate. In Schizocliiton they are arranged in very symmetrical 

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

 two, sometimes only one, on the central ]3lates. In Tonicia 

 marmorata the eyes are sunk in little cup-shaped depressions 

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

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

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

 . Gh. aculeatus they are oval, measuring about -^^ X ^-^y inch. 

 There are no eyes in Chiton proper, nor in MojKdia, 3favf/eria, 



