714 William Patten 



energy. This supposition of course rests entirely upon our former 

 conclusion that animai pigment in general performs a physiological 

 function, and like Chlorophyll, absorbs energy from the sunlight. 



This conclusion appears more reasonable to us on account of the 

 many difficulties which may thus be accounted for , as well as the im- 

 possibility of explaiuing these difficulties in any other manner known 

 to US. In the first place, I believe that no explanation of the function 

 of the ocelli in Coelenterates , Echinoderms , and in such Mollusca as 

 Chiton^ Onchidium, and Area, will be of any value, which does not in- 

 clude the ocelli or pigment spots of Protozoa and plant zoospores. Now 

 to suppose that these ocelli simply distinguish light from darkness is 

 absurd, for we cannot in any case suggest any reasonable necessity for 

 such a power. No one can fail to be impressed by the interesting ex- 

 periments of Romanes, who has shown that Medusae will collect with 

 great avidity around a ray of sun-light entering a darkened jar. No 

 one would suppose that they enter the light in order to see it! But ou 

 the contrary because they receive some benefit from it. But 

 how can this benefit be any other than that received by plants from the 

 sunlight, i.e. energy? Surely no Medusa could escape its enemies or ob- 

 tain its food any easier with ocelli than without them. But it is possible 

 that it might be able to distinguish with them whether it is at the sur- 

 face or at a considerable depth , and could then sink to avoid storms, 

 or rise to obtain food. But if we apply this reasoning to Arca or Pectun- 

 culus, it will not work, since both are incapable of motion, while Arca 

 is permanently attached by its byssus. Neither can it be shown that 

 Onchidium uses its innumerable eyes to escape its enemies — in spite 

 of the reasoning of Sempek — or to obtain its food. The same diffi- 

 culties apply to Chiton, which is also provided with innumerable eyes 

 in ali stages of development; and there can be no doubt that there are 

 many more animals, as yet imperfectly known, which possess so-called 

 eyes as numerous and as anomalous as those found in Chiton, Onchi- 

 dium, Arca, Pectimculus, Cardium and Pecten, as well as those of many 

 Echinoderms and Coelenterates. 



A supposed explanation of these eyes, widely current and apparent- 

 ly generally accepted, is that they are organs for the perception of beat, 

 and that by graduai changes they developed into organs for the per- 

 ception of light. But I believe it would be perfectly safe to challenge 

 any one to show what advantage it would be for a Protozoan , Coelen- 

 terate, or Mollusc, to perceive beat' This theory arose from the fre- 

 quent presence of black pigment in many less complicated eyes , and 



