480 THE NERVE DISTRIBUTION IN THE EYE OF PECTEN IRRADIANS. 



extremely complex nor the internal relations of its structural elements as complicated 

 as was supposed. Making allowances for the fact that different species have been 

 studied I believe that the previous descriptions and interpretations of the retinal cells 

 in Pecten are in some important particulars misleading, a condition of affairs that has 

 been partly remedied by the employment of new methods. 



VI. CONCLUSIONS. 



1. I conclude that the rods have been inadequately described, and that they 

 are not innervated by fibres from at least three series of nerves. 



2. The so-called retinophorse are not the visual sensory cells whose peripheral 

 fibres form the basal optic nerve, but they are the supporting cells of the median layer 

 of the retina. 



3. The inner ganglionic cells do not connect with the side branch of the optic nerve, 

 but are the nerve-cells of the bipolar nerve elements. 



4. The outer ganglionic cells form a single layer whose inner fibres are disposed 

 in a special reticular structure in the retina and whose outer fibres make direct con- 

 nection with the side branch of the optic nerve. 



5. The existence of the large marginal ganglionic cells and their relations to the 

 bipolar and optic nerve were not known to other investigators of the eye of Pecten. 



6. I believe that the visual apparatus of the retina is composed of afferent and 

 efferent neurones, and agree with von Lenhossek ('96) that the rods are true per- 

 ipheral visual neurones. The distal ends of their axons represent, therefore, retinal 

 sensory endings. Their proximal terminal spherules and the terminal tufts of the 

 afferent axon of the bipolar cells establish conduction relations between rods and 

 bipolar cells, and by means of the efferent axons of the latter connection is made with 

 the marginal ganglionic cells. Through the latter and their nerve-fibres impulses 

 are thus transmitted from the rods through the bipolar cells and marginal ganglionic 

 cells to the brain. The efferent paths are, I believe, through the side branch of the 

 optic nerve to the external ganglionic cells and their efferent beaded fibrils. The 

 latter, due to their method of branching, have an arborescent appearance in the median 

 layer, and as finest fibrils terminate in tiny flat nodules on the different retinal elements. 



