ON THE EYES QF SOME IHVBRTEBRATA, 673 



On the Eyes of Some Inv^ertebrata, 



By 



Justus Carriere, 



Of Strassburs:, 



With Plate XLV. 



It is known that in the Vertebrata the percipient elements 

 of the retina turn away from the light, while they are turned to 

 it in the Invertebrata — an arrangement which is conditioned 

 by the development of the organ in both the groups. 



In order to attain the greatest efifect and to embrace a very 

 extended horizon the percipient elements can be arranged in 

 two ways. 



Either they form the wall of a hollow ball, into which the 

 light falls through a very small opening, so that there is sketched 

 a real image on the background of the eye. This kind of organ 

 of sight is found in the vertebrates and the cephalophorous 

 molluscs and lies below the surface of the body. 



Or the parts of the eye perceiving the light are radially dis- 

 posed on a more or less complete ball, which projects beyond 

 the surface of the body. These eyes, forming a fan in vertical 

 section, are met with among the Arthropoda and certain 

 Lamellibranchiata. 



A third form of eyes which belongs to the Arthropoda, the 

 cup-shaped eyes with one lens, will not be considered in the 

 present communication ; nor will the organs of sight constructed 

 upon the principle of the camera obscura be dealt with, since 

 my purpose is merely to offer a few remarks in regard to fan- 

 shaped (coniform) eyes. 



Through Grenacher we know the construction of the eyes 



