458 Benjamin Sharp 



ciate the fact by the growing intensity of the light, and by that peculiar 

 flapping motion of the valves the Pectens are so remarkable for, move 

 away into deeper water« ' . 



This theory may at once be set aside when we consider that the 

 Pectens of the Mediterranean, where we have praetically no tide at all, 

 a State of affairs that has existed for an exeeedingly long period of 

 time, have as well developed eyes as those found on shores where tides 

 do exist ; and further it seems hardly probable that such a complicated 

 organ would have developed to determine for the animai, whether it be 

 out of water or not. 



Now I am inclined to believe, as.has been siiggested by Hensen^, 

 that the pigmented epithelial cells that cover this organ and the stalk 

 on which it is situated , and the only place where we find a marked 

 deposit of pigment, is the seat of vision for these animals and that the 

 so- called eye may be an organ of some other sense , as suggested by 

 Schmidt 3. If this supposition be correct we should have the sense of 

 vision of the same grade as that of other Lamellibranchs. If the organ 

 in question is so highly developed , we must necessarily conclude that 

 vision, if this be the sense, is also highly developed, which does not 

 appear to be the case. And were this organ an eye of high grade its 

 advantage to the animai could not be very great, as the food and safety 

 of the animai does not require such perfected vision. The pigmented 

 cells (flg. 15) with the refractive ends, seem to answer the limited 

 vision that they possess. 



As regards the complicated organ known as the eye, I might sug- 

 gest that, if this be an eye, it is one where we have no true pigmented 

 layer in any direct relation to either the nerve or the retina. The mass 

 of red pigment and the metallic-like tapetum would hardly answer the 

 place of the black choroid coat so esseutial to the eye. 



Fani. Limiclae, 



The species of Lima examined by Grube is not given neither does 

 he consider the anatomy of the eye. He merely states that Pecten and 

 Lima are the only Lamellibranchs that can see, and then considers 

 only the anatomy of the eye of Pecten. 



The tentacles fringing the border of Lima squamosa, the only 



1 S. J. HiCKSON, The eye o{ Pecten etc. 1880. p. 454. 



2 V. Hensen, Über das Auge einiger Cephalopoden etc. 1865. p. 221. 



3 E. 0. Schmidt, Handbuch der vergleich. Anatomie etc. 1882. p. 181. 



