THE EYE OP PECTEN. 71 



and stained in Heidenhain's iron liaematoxylin, a remarkable 

 structure. In addition to the nucleus there was present a 

 dark staining body from which delicate but very distinct 

 fibrils radiated out to the periphery and became attached to 

 the cell-wall. Most of them were straight, some were bent, 

 hut all went out from the one point and all could be followed 

 to the cell membrane if their whole length lay in the section. 

 I have found the same structures (PI. 7, fig. G, h.), not only in 

 material fixed and stained as above but also after the 

 followino- treatment: 



After fixation in Hermann-sublimate mixture and staining 

 in iron hfematoxylin, the shape of the cells is well preserved, 

 the contents are homogeneous or very finely granular and 

 stain grey, the nucleus is black, and radiating fibrillse appear 

 distinctly in many cells though not in all. After Zenker 

 fixation and Mallory's stain the cell contents are very granular 

 in appearance and stained deep red, the nuclei being yellow- 

 red, and there is just a slight trace of the fibrillae. They are 

 also to be made out, though not distinctly, after Bouin fixa- 

 tion. Von Rath's treatment caused the cell contents to 

 appear very granular and vesicular (PI. 7, fig. 6, d.) the radi^ 

 ating fibrillse were often very distinct, but the central dark 

 staining body did not look exactly like the normal centrosome 

 of dividing cells. 



This permanent centrosome (PI. 7, fig, 6, Cent.), if it be such, 

 does not appear to have any definite position, but since it 

 cannot be made out in macerations it is almost impossible to 

 determine its true position, for sections cut the cells in all 

 directions. In addition to the species enumerated by Hesse 

 I have found these structures in P. tenuicostatus, and 

 probably they are present in all species. Hesse naturally 

 compared these Avith the centrosome and astral rays which 

 appear in cells undergoing mitotic division. Such structures 

 have been demonstrated as persisting in the resting stages 

 of certain cells, in pigment-cells of fishes, and more particularly 

 in leucocytes. It has not been possible for Hesse or myself 

 to determine any connection Avith cell-division. The astral 



