THE EYE OP PECTEN. 51 



fully when describing the structures involved, and it will 

 avoid repetition if they be omitted here. In 1795 Poli, in his 

 large Avork on the Mollusca (1), gave figures illustrating the 

 general anatomy of Pecten, in which the eyes are depicted, 

 and also a view of the mantle-edge showing more clearly the 

 tentacles and eyes, but no details of structure are given what- 

 ever except the external pigmented ring bounding the cornea 

 and the pigment stripe on the tentacles. 



He recognised a likeness to the human eye, and as usual 

 applied some of the names given to parts of the latter, a 

 feature followed by his successors, who naturally recognised 

 at once the resemblance to the vertebrate eye, which is such 

 a striking character of the eyes of Pecten, These orgaus 

 were mentioned, though left practically undescribed by suc- 

 ceeding naturalists. Cuvier refers to them as "globules 

 verdatres," and Lamarck as " tubercules oculif ormes." 



The next description is to be found in Robert Grant's 

 'Comparative Anatomy' (2), where reference is made to the 

 ''smooth cornea," the "iridescent choroidea," and a "small 

 crystalline lens," Another English writer, Robert Garner (3), 

 1837, continued the work. He states that Pecten, Spondylus, 

 andOstrea (probably Pecten jacobseus, Ostrea jacobseus 

 of Poli) possess " small, brilliant, emerald-like ocelli, which, 

 from their structure, having each a minute nerve, a pupil, a 

 pigmentum, a striated body, and a lens, and from their situa- 

 tion at the edge of the mantle, where alone such organs could 

 be useful, and also placed, as in Gasteropoda, with the 

 tentacles, must be organs of vision." There are no figures 

 illustratinghis short account. Almost simultaneously Krohn (5) 

 and Grube (4) published descriptions of the eye. Grube des- 

 cribed the position and number of the eyes in P. jacoba3us, 

 P. varius, and P. opercularis. Krohn gave a much more 

 detailed account. He stated that the eye was a closed 

 spherical vesicle containing two transparent bodies separated 

 by a septum (he was therefore the first observer to see this 

 structure). The hinder of these bodies he described as being 

 of fibrous texture. Krohn was the first investigator to notice 



