1905.] NATURAL SCIENCES OF PHILADELPHIA. 135 



nerve fibres from the ommatidia form a relatively compact mass and 

 the retiniilar ganglion cells are scattered through the fibres in such a 

 way as to have the appearance of a definite ganglion. The nuclei of 

 the retinular ganglion are no longer nearly in one plane, but are scat- 

 tered for a considerable distance between the basement membrane 

 and the outer fibrillar mass due to the crowding of the nerve fibres. 



The question naturally arises as to the number of cells of the retinular 

 ganglion as compared with the number of ommatidia. A count is, 

 of course, impossible, but careful examination reveals that there can- 

 not be many more than one to an ommatidium, certainly not one to 

 each retinular cell. The eight nerve fibres from each group of retinular 

 cells are entirely separate, but lie close together, so that probably one 

 and only one retinular ganglion cell receives the impulse carried from 

 the retina on eight nerve processes, and consecutive cross-sections indi- 

 cate that the eight nerve fibrils surround the thick part of the retinular 

 ganglion cell where the nucleus is located and transmit the impulse by 

 contact. 



In his description of this region Kenyon says:^ "The elements 

 from the retina terminate each in a small tuft of fine branches in the 

 outer fibrillar body, and come in contact with the fine lateral branchlets 

 given off in the same region by fibres originating from the cells of Ber- 

 ger's granular layer (retinular ganglion)." The tuft of fine branches 

 here mentioned are the separate nerve fibres from the retinulae. I have 

 been unable to see the fine branches of the retinular ganglion cells. 



The retinular ganglion cell in turn sends in its fibre through the first 

 fibrillar mass, and then through the outer chiasma to the opposite 

 side of the group of ganglia, where the impulse is given over to a cell 

 of the first optic ganglion. From here on the tracing of the fibres 

 requires special nerve methods which were not employed in this work. 

 However, this much is evident : the cells of the first optic ganglion send 

 their fibres through the second fibrillar mass and through the inner 

 chiasma to the second optic ganglion, where the impulse is probably 

 again transferred to another cell which, in turn, carries it to the brain. 

 The course of these fibres has been worked out in detail by Kenyon 

 (1897), and in my work I find nothing to contradict his results, although 

 the methods used in my work were not such as to warrant either a 

 positive denial or confirmation of his work. 



»P. 374. 



