On the Visual Organs in Lamellibranchiata. 



Benjamin Sharp, Dr. med. et phil., 



Professor of the Lower Invertebrata at tlie Academy of Natural Sciences of PMladelpMa, ü. S.A. 



With Piate 26. 



Introduction. 



My attention was first drawn to this subject by obsemng a number 

 of Solen vagina which were exposed for sale in large basins at Santa 

 Lucia in Naples. By passing my band over the basiu I noticed that 

 those Solen upon whicli the shadow of my band feil . instantly witb- 

 drew their siphons, while tbose not toucbed by tbe shadow remained as 

 before, immovable. Obtaining some specimens at the Zoological Station 

 I repeated the experiment and was convinced that the animals possessed 

 some power of distinguishing light from darkuess. This led me to 

 examine the minute strueture of the siphon carefully and my search 

 was rewarded by the discovery of a very primitive form of visual organ, 

 so primitive in faet that the term eye can hardly be applied to it. 



I wish bere to extend my thauks to the Bavarian Government for 

 allowing me tbe use of its table during the months of March, April and 

 May of 1883 and also to the director, Professor A. Dohkx, and bis assist- 

 ants at the Zoological Station , while in the pleasant company of the 

 latter I received much advice and assistauce. 



Part of the material only came from Xaples namely Solen vagina, 

 Pecten Jacohaeus , Patella coerulea , and Haliotis tuherculata. Solen 

 ensis , Vetius mercenaria, Ostrea virginica and Mac fra solidissima 

 carne from the coast of New Jersey, U. S. A., and Mya arenaria from 

 Boston, Mass., U. S. A. The specimens of Anomia ephippium and 

 Mytilus edulis I collected at Villafranca, France. I am indebted to tbe 

 curators of the Acad. of Nat. Sc, for the use of all other material. 



