On the Visual Organs in Lamellibranchiata. 455 



As regards the other species that I have examined — Ostrea eduUs, 

 I may say that we have essentially the same state of affairs here as in 

 O. virginica. I foimd no evidence of differentiated eyes on the mantle 

 edge, that have been spoken of by former writers on the subject. This 

 is probably the form that the European writers have investigated. 



Farn. Anoniidae. 



Anomia ephippium has according to Siebold twenty brown sessile 

 eyes situated between the numerous tentacles. In this as in the pre- 

 ceding form I was unable to find any evidence of a differentiated eye. 



The mantle, which is capable of being contracted to a considerable 

 distance within the shell , is densely set with tentacles. The upper 

 border of the mantle is strongly pigmeuted and thrown into regulär 

 folds; from the bases of these folds spring the non-pigmented ten- 

 tacles , thus causing the pigmented surface to round up , and this is 

 what Siebold mistook for the sessile eyes. On the lower borderà we 

 find scarcely any pigment at all, and this side of the mantle forms a 

 strong contrast with the opposite mantle border. The pigment that is 

 present in the lower border is collected into little spots lodged at the 

 bases of the numerous folds into which the mantle is thrown. The ten- 

 tacles here are also not pigmented and are about as numerous as they 

 are on the upper border. 



These small dots of pigment may also have been mistaken for 

 eyes by Siebold. 



Now by carefully examining a series of sections of the mantle bor- 

 der I found no trace of »sessile eyes«. The pigment is black and in very 

 regulär spherical granules deposited only in the epithelial cells. The 

 characteristic refracting cuticle is present, but not so distinct as in 

 Ostrea. 



I have unfortunately no experimental evidence in this species, that 

 any visual power is present , but from the form of the cells and that 

 Siebold supposed eyes to be present, I think I can safely assume that 

 such is the case. 



Fani. Bectinidae. 



Pecten. The species of this family have been generally those taken 

 for the investigation of the eye among the Lamellibranchiata , and the 



1 I use the term upper and lower, instead of right and left for convenience. 

 The term lower being that which is on the shell, which is attached to the foreign 

 body. 



