EYES OF MOLLUSCS. 359 



for specific purposes. A function there must be, and 

 doubtless a good one ; but we speak with large latitude 

 of anthropomorphism when we speak of the " vision " 

 of these animals. JMolluscan vision is not human 

 vision ; nor in accurate language is it vision at all : it 

 is not seeing, but feeling; it is not a perception of 

 objects, but a sensation of light and darkness. This 

 does not apply to the Cephalopoda, in which vision 

 seems to be as perfect as in Fishes ; nor, on the other 

 hand, does it apply to those Bivalves which have no 

 eyes at all, not even " eye-specs." The word Mollusc 

 embraces a vast variety ; and, by way of limitation, the 

 reader must understand that the following remarks are 

 confined to those genera which I have directly studied 

 for the purpose — Doris, Eolis, Pleurobranchus, and 

 Aplysia. In the three first genera the eyes are under- 

 neath the skin and muscles, and rest on the brain 

 (oesophageal ganglia), attached thereto by a microsco- 

 pic nerve. There is no apertm-e in the skin, as there is 

 in ours, through which the rays of light may fall directly 

 on the eye ; so that in spite of pigment, lens, and nerve 

 — the essential parts of a visual organ — vision is 

 utterly impossible ; as you may convince yourself even 

 with your own admirable eyes, if the lids are obsti- 

 nately closed over them. I am aware that clairvoyants 

 of the strictly unveracious species, profess to see with 

 their eyes closed ; but our simpler Molluscs have no 

 such pretensions ; they have not yet given in to the 

 claii^voyant mania, and are content to submit to those 

 laws of physics which regulate phenomena with the 



