On the Visual Organs in Lamellibranchiata. 459 



species tliat I liave had opportimity to examine are comparatively very 

 long, but have no pigment deposited in tbem whatever ; neither could I 

 find any trace of pigment at the bases of the tentacles to sustain the 

 fact that, according to Grube, Lima can see. 



Farn. Spondylidae. 



The investigators who have mentioned that Spondylus possess eyes 

 are Poli, Garner, Will, and Hickson. The only one who entered 

 upon the anatomy and histology was Hickson , who finds the form of 

 the organ essentially the same as the so-called eye oiPecten. The spe- 

 cies investigated by Poli was Spondylus gaederopus^ the other authors 

 did not give the specific name. 



Althongh it has not been mentioned whether the pigmented cells 

 of the epiderrais of the eye and stalk of Spondylus are capped with a 

 refractive cuticiila , I feel qiiite sure in stating that such exists , as the 

 Organs are so similar in every respect to those of Pecten. Hickson did 

 not observe them even in Pecten and consequently did not mention it, 

 in the short account of Spondylus. 



Farn. I*innida€. 



I am unable to find out the species investigated by Will and Sie- 

 bold and further have not had the opportunity of examining any spe- 

 cimens. Vision is no doubt present as the observations of Will and 

 Siebold are supported by Gegenbaur , but I am very doubtful, if any 

 complicated organ is present. 



Fam. Aviculidae. 



I have had the opportunity of examining a species of Avictda from 

 Panama [A. stertia?). As far as I know this genus has never been in- 

 vestigated as regards vision and so I have no experimental proof of 

 such. The whole edge of the mantle is well furnished with tentacles, 

 at the bases of which are found well defined pigmented grooves. On 

 the cone-shaped tentacles about half-way up was found a pigmented 

 band, that extended around the cone and in breadth was about equal to 

 half the height of the cone. 



These conish tentacles were comparatively short and measured 

 from about 1 mm to 2,5 mm in length. I could find no trace of special- 

 ized eyes. I am inclined to belle ve that these pigmented grooves and 

 bands answer the purpose of vision. The animai was not in a fit con- 

 dition to settle the question by sections, and so I have to conclude from 



