448 MR FRANK E. BEDDARD ON THE STRUCTURE OF 



downwards to encircle the rhabdom. This being the case, what cells do form 

 the rhabdom? It appears that Grenacher has already solved this problem, 

 and that his retinula cells give rise to the rhabdom. In my preparations of 

 the eyes of the Serolidre and CymothoidaB I can find no reason for doubting 

 that the rhabdom is a product of the retinula cells; the absolute continuity 

 between the retinula cells and the rhabdom is illustrated in fig. 12, and the 

 same figure shows that the division of the rhabdom into seven radially- dis- 

 posed rhabdomeres corresponds with the number (seven) of the retinula cells. 

 In view of these facts, it is hard to believe that the rhabdom is anything else 

 than the chitinous secretion of the retinula cells. 



So far my results are confirmatory of those of Grenacher and at variance 

 with those of Patten. But it must always be borne in mind that Patten has 

 not investigated the Isopod eye. 



The nature of the remarkable hyaline cells present in the Cymothoidse and 

 in the Serolida? now remains to be considered. 



The large size of these cells plainly indicates that they are of some import- 

 ance in the eye. 



In seven of my figures of the eye of Serolis I have indicated a delicate fila- 

 ment (r 7 ) passing* out from between the two hyaline cells, running back towards 

 the membrane bounding the ommateum; I have since re-examined my sections 

 and teased preparations of the eye of Serolis cornuta and S. schythei, and find 

 that this structure is nearly invariably present; I have succeeded in finding it 

 in so many cases that I am inclined to believe it is in reality always present. 

 I have traced the filament through the hyaline cells, at the upper end of which 

 it becomes frayed out into a spindle-shaped bundle of fibrils; the exact mode of 

 termination of these I have not been able to ascertain; they seemed to pass up 

 into the axis of the rhabdom. In the paper referred to I have asserted their 

 continuity with the rhabdom; a renewed examination of my preparation enables 

 me, on the whole, to confirm this statement; they always appeared to end 

 in the way described. I have re-drawn isolated elements of the eye 

 of Serolis cornuta and S. schythei, in order to illustrate the above-described 

 facts (figs. 1, 2, 3.). Fig. 3 illustrates an element of the eye of S. cornuta; 

 figs. 1, 2 an isolated element of the eye of S. schythet, in this latter species 

 there are two hyaline cells present, and the filaments passing down from the 

 lower extremity of the rhabdom can be easily seen by careful focussing to pass 

 through the substance of these cells. In S. cornuta also there are clearly two 

 hyaline cells present. 



The bundle of delicate fibrils which appear to start from the rhabdom 

 unite a little way from the rhabdom, but still in the interior of the hyaline cell 

 or cells, into a single thread, which certainly reaches as far as the membrane 



* Loc. cit., pi. ix. figs. 3, 4, 5. 



