568 William Patten 



simply leiterates the Statements of Will, as do also Schmidt (17) and 

 Gegenbaur (14) . Carrière's (19) recent description, accompanied by 

 a drawing-, is of little importance, siuce it coutains notliing- new but 

 what is wrong, and nothing right that was not already known. The 

 description given of the finer anatomy of the faceted eyes of Arca will, 

 with the exception of the slight differences already mentioned. apply 

 equally well to Pectunculus. 



Pecten. 



Historical. 



It is not to be expected that the remarkable organs, which we shall 

 bere consider, so prominent and so brilliantly colored, could bave long 

 escaped the attention of the older Naturalists. 



Nearly a Century has elapsed since they were first described by 

 Poli (1), in 1795, who noticed their arrangement in pairs (a fact over- 

 looked by subsequent writers) and their position at the ends of short ten- 

 tacles ; he thus unwittingly introduced the theory that they were modified 

 tentacles , an opinion held by some even to the preseut day. He could 

 hardly bave failed to recognize the resemblance of these organs to the 

 human eye, as in fact he did, and applied corresponding names to 

 what he considered to be corresponding parts. This had its effect upon 

 succeeding writers, — to whom the terms homology and analogy were 

 unknown, — who, upon the discovery of new parts, saw in them the 

 strnctures known to occur in the human eye. To them there was but 

 one visual organ, that of the Vertebrates, and. having once recog- 

 nized in the eye of Pecten a superficial resemblance to that of the Ver- 

 tebrates, they believed that there must be a corresponding agreement 

 in ali the remaining parts. This led to results which, as far as Pecten 

 is concerned , are less striking , since there is indeed a remarkable 

 agreement in more ways than one ; but in less complicated visual or- 

 gans, such as described by Will for otherLamellibranchiata, where the 

 so-called eyes in reality cousist of hardly more than pigment spots, one 

 is surprised to learn that in these simple organs they were able to re- 

 cognize a lens, vitreous bod}^, choroid. iris etc., all of which are terms 

 borro wed from human anatomy. 



Although it appears that the existence of these minute eyes was 

 not forgotten, further mention of them was not made until 1837, when 

 Robert Garner (2) described the »Brilliant emerald-like ocelli, which 



