450 MR FRANK E. BEDDARD ON THE STRUCTURE OF 



Now the rhabdom of the young eye is so closely similar in every particular 

 to the peculiar axial structure (figs. 1, 2, 2r') of the adult eye, that it seems 

 impossible to come to any other conclusion than that they are identical. 



Although the retinula cells are easily freed from the axial bundle of fibrils, 

 the latter are not left in such preparation entirely denuded ; they are, in fact, 

 seen to be surrounded by a variable amount of granular matter, and near to 

 the lower end of the conical body one or two nuclei were occasionally to be 

 seen. These nuclei, as illustrated in the figure, differ in their characters from 

 the nuclei of the retinula cells. Sometimes only one was to be seen, but in 

 this case it invariably lay to one side of the axial cone, indicating that the 

 other nucleus had been present, but had been lost in the process of teasing up 

 the material ; when both nuclei were present they were seen to be symmetri- 

 cally disposed towards one another, and to lie on either side of the extremity of 

 the axial- cone. 



In transverse sections of the young eye (fig. 18) these nuclei are distinctly 

 visible, and it is possible that the cells to which they belong, which are 

 evidently the hyaline cells of the adult eye, take some share in the formation of 

 the rhabdom. 



In any case the rhabdom of the young ommatidium is evidently principally 

 formed by the retinula cells, for in transverse sections (figs. 17, 18) it is seen to 

 be four-sided, in correspondence with the four retinula cells. 



The structure which I have termed the rhabdom in the adult eye (r, figs. 1, 

 2, 3, &c.) appears to be therefore a new structure, differing somewhat in its 

 character from the rhabdom of the young eye, which, however, persists although 

 very inconspicuous. 



It will not escape the attention of those who have read Dr Patten's paper, 

 that these hyaline cells bear not a little resemblance to his " retinopho?'w." One 

 of the principal positions which he takes up with respect to the invertebrate 

 eye is, that the cells which are immediately concerned in the function of vision 

 are colourless cells, and contain a network of nerves. These colourless cells are 

 grouped in various numbers, and each group is separated from a neighbouring 

 group by circles of pigment cells, which he terms retinula, among which the 

 retinula of Grenacher form only one series. 



In identifying a clear colourless cell or cells in each retinula, my results agree 

 with those of Patten. With regard to the Arthropod eye, however, the agree- 

 ment between my results and those of Patten end here. The retinophorae, accord- 

 ing to that author, form the crystalline cone and the rhabdom, which is merely 

 a continuation of it. The hyaline cells of Serolis, &c, are plainly distinct from 

 the cells which form the crystalline cone, and they do not form the rhabdom. 

 At present, therefore, I am unable to compare the eye of Serolis and the 

 Cymothoidse with the eye of the Decapoda and Insects as interpreted by Patten, 



